diff --git a/.gitignore b/.gitignore
index 4bcc6612..4bc5bde0 100644
--- a/.gitignore
+++ b/.gitignore
@@ -52,4 +52,12 @@ _ReSharper*/
 ~$*
 
 #NuGet
-packages/
\ No newline at end of file
+packages/
+.idea/.idea.EPPlus/.idea/contentModel.xml
+.idea/.idea.EPPlus/.idea/encodings.xml
+.idea/.idea.EPPlus/.idea/indexLayout.xml
+.idea/.idea.EPPlus/.idea/misc.xml
+.idea/.idea.EPPlus/.idea/modules.xml
+.idea/.idea.EPPlus/.idea/vcs.xml
+.idea/.idea.EPPlus/.idea/workspace.xml
+.idea/.idea.EPPlus/riderModule.iml
diff --git a/EPPlus/Drawing/Vml/ExcelVmlDrawingCommentCollection.cs b/EPPlus/Drawing/Vml/ExcelVmlDrawingCommentCollection.cs
index d10f0af7..9dd780d8 100644
--- a/EPPlus/Drawing/Vml/ExcelVmlDrawingCommentCollection.cs
+++ b/EPPlus/Drawing/Vml/ExcelVmlDrawingCommentCollection.cs
@@ -113,7 +113,15 @@ private XmlNode AddDrawing(ExcelRangeBase cell)
             {
                 ix = ~ix;
                 var prevDraw = _drawings[ix] as ExcelVmlDrawingBase;
-                prevDraw.TopNode.ParentNode.InsertBefore(node, prevDraw.TopNode);
+                var parentNode = prevDraw.TopNode.ParentNode;
+                if (parentNode!=null)
+                {
+                    parentNode.InsertBefore(node, prevDraw.TopNode);
+                }
+                else
+                {
+                    VmlDrawingXml.DocumentElement.AppendChild(node);
+                }
             }
             else
             {
diff --git a/EPPlus/EPPlus.csproj b/EPPlus/EPPlus.csproj
index 1f411ce0..00b7eafb 100644
--- a/EPPlus/EPPlus.csproj
+++ b/EPPlus/EPPlus.csproj
@@ -25,7 +25,7 @@
     <UpgradeBackupLocation>
     </UpgradeBackupLocation>
     <OldToolsVersion>3.5</OldToolsVersion>
-    <TargetFrameworkVersion>v3.5</TargetFrameworkVersion>
+    <TargetFrameworkVersion>v4.0</TargetFrameworkVersion>
     <PublishUrl>publish\</PublishUrl>
     <Install>true</Install>
     <InstallFrom>Disk</InstallFrom>
diff --git a/EPPlus/ExcelCommentCollection.cs b/EPPlus/ExcelCommentCollection.cs
index 9835142f..3b68d9d7 100644
--- a/EPPlus/ExcelCommentCollection.cs
+++ b/EPPlus/ExcelCommentCollection.cs
@@ -218,10 +218,15 @@ public void Remove(ExcelComment comment)
             }
             if (comment==c)
             {
-                comment.TopNode.ParentNode.RemoveChild(comment.TopNode); //Remove VML
-                comment._commentHelper.TopNode.ParentNode.RemoveChild(comment._commentHelper.TopNode); //Remove Comment
+                //
+                comment.TopNode.ParentNode?.RemoveChild(comment.TopNode); //Remove VML
+                comment._commentHelper.TopNode.ParentNode?.RemoveChild(comment._commentHelper.TopNode); //Remove Comment
+
+                if (Worksheet.VmlDrawingsComments._drawings.ContainsKey(id))
+                {
+                    Worksheet.VmlDrawingsComments._drawings.Delete(id);
+                }
 
-                Worksheet.VmlDrawingsComments._drawings.Delete(id);
                 _list.RemoveAt(i);                
                 Worksheet._commentsStore.Delete(comment.Range._fromRow, comment.Range._fromCol, 1, 1, false);   //Issue 15549, Comments should not be shifted 
                 var ci = new CellsStoreEnumerator<int>(Worksheet._commentsStore);
diff --git a/EPPlus/ExcelRangeBase.cs b/EPPlus/ExcelRangeBase.cs
index 0519de60..50921ec2 100644
--- a/EPPlus/ExcelRangeBase.cs
+++ b/EPPlus/ExcelRangeBase.cs
@@ -253,11 +253,11 @@ private static void Set_StyleName(ExcelRangeBase range, object value, int row, i
         private static void Set_Value(ExcelRangeBase range, object value, int row, int col)
         {
             var sfi = range._worksheet._formulas.GetValue(row, col);
-            if (sfi is int)
+            if (sfi is int && !range.IsSingleCell)
             {
                 range.SplitFormulas(range._worksheet.Cells[row, col]);
             }
-            if (sfi != null) range._worksheet._formulas.SetValue(row, col, string.Empty);
+           // if (sfi != null) range._worksheet._formulas.SetValue(row, col, string.Empty);
             range._worksheet.SetValueInner(row, col, value);
         }
         private static void Set_Formula(ExcelRangeBase range, object value, int row, int col)
@@ -1270,7 +1270,11 @@ public bool Merge
             set
             {
                 IsRangeValid("merging");
-                _worksheet.MergedCells.Clear(this);
+                if (!_worksheet.DisableMergeValidation)
+                {
+                    _worksheet.MergedCells.Clear(this);
+                }
+
                 if (value)
                 {
                     _worksheet.MergedCells.Add(new ExcelAddressBase(FirstAddress), true);
@@ -1608,7 +1612,7 @@ private void SplitFormula(ExcelAddressBase address, int ix)
             //The formula is inside the currenct range, remove it
             if (collide == eAddressCollition.Equal || collide == eAddressCollition.Inside)
             {
-                _worksheet._sharedFormulas.Remove(ix);
+               // _worksheet._sharedFormulas.Remove(ix);
                 return;
                 //fRange.SetSharedFormulaID(int.MinValue); 
             }
@@ -2609,29 +2613,35 @@ public void Copy(ExcelRangeBase Destination, ExcelRangeCopyOptionFlags? excelRan
             }
             var copiedMergedCells = new Dictionary<int, ExcelAddress>();
             //Merged cells
-            var csem = new CellsStoreEnumerator<int>(_worksheet.MergedCells._cells, _fromRow, _fromCol, _toRow, _toCol);
-            while (csem.Next())
+
+            for (var row = _fromRow; row <= _toRow; row++)
             {
-                if (!copiedMergedCells.ContainsKey(csem.Value))
+                for (var col = _fromCol; col <= _toCol; col++)
                 {
-                    var adr = new ExcelAddress(_worksheet.Name, _worksheet.MergedCells.List[csem.Value]);
-                    var collideResult = Collide(adr);
-                    if (collideResult == eAddressCollition.Inside || collideResult == eAddressCollition.Equal)
-                    {
-                        copiedMergedCells.Add(csem.Value, new ExcelAddress(
-                            Destination._fromRow + (adr.Start.Row - _fromRow),
-                            Destination._fromCol + (adr.Start.Column - _fromCol),
-                            Destination._fromRow + (adr.End.Row - _fromRow),
-                            Destination._fromCol + (adr.End.Column - _fromCol)));
-                    }
-                    else
+                    var key = _worksheet.GetMergeCellId(row, col) - 1;
+                    if (key >= 0 && !copiedMergedCells.ContainsKey(key))
                     {
-                        //Partial merge of the address ignore.
-                        copiedMergedCells.Add(csem.Value, null);
+                        var adr = new ExcelAddress(_worksheet.Name, _worksheet.MergedCells.List[key]);
+                        var collideResult = Collide(adr);
+                        if (collideResult == eAddressCollition.Inside || collideResult == eAddressCollition.Equal)
+                        {
+                            copiedMergedCells.Add(
+                                key,
+                                new ExcelAddress(
+                                    Destination._fromRow + (adr.Start.Row - _fromRow),
+                                    Destination._fromCol + (adr.Start.Column - _fromCol),
+                                    Destination._fromRow + (adr.End.Row - _fromRow),
+                                    Destination._fromCol + (adr.End.Column - _fromCol)));
+                        }
+                        else
+                        {
+                            //Partial merge of the address ignore.
+                            copiedMergedCells.Add(key, null);
+                        }
                     }
                 }
             }
-
+            
             Destination._worksheet.MergedCells.Clear(new ExcelAddressBase(Destination._fromRow, Destination._fromCol, Destination._fromRow + toRow - 1, Destination._fromCol + toCol - 1));
 
             Destination._worksheet._values.Clear(Destination._fromRow, Destination._fromCol, toRow, toCol);
diff --git a/EPPlus/ExcelStyles.cs b/EPPlus/ExcelStyles.cs
index 79708310..cfdc8a20 100644
--- a/EPPlus/ExcelStyles.cs
+++ b/EPPlus/ExcelStyles.cs
@@ -953,6 +953,7 @@ internal int CloneStyle(ExcelStyles style, int styleID, bool isNamedStyle, bool
                     xfs = style.CellXfs[styleID];
                 }
                 ExcelXfs newXfs = xfs.Copy(this);
+                newXfs.XfId = 0;
                 //Numberformat
                 if (xfs.NumberFormatId > 0)
                 {
@@ -1026,7 +1027,7 @@ internal int CloneStyle(ExcelStyles style, int styleID, bool isNamedStyle, bool
                 }
 
                 //Named style reference
-                if (xfs.XfId > 0)
+                if (isNamedStyle && xfs.XfId > 0)
                 {
                     var id = style.CellStyleXfs[xfs.XfId].Id;
                     var newId = CellStyleXfs.FindIndexByID(id);
diff --git a/EPPlus/ExcelWorkbook.cs b/EPPlus/ExcelWorkbook.cs
index 0887bd35..f7880b24 100644
--- a/EPPlus/ExcelWorkbook.cs
+++ b/EPPlus/ExcelWorkbook.cs
@@ -175,6 +175,11 @@ internal void GetDefinedNames()
 				{ 
 					string fullAddress = elem.InnerText;
 
+                    if(fullAddress.EndsWith("!#REF!"))
+                    {
+                        continue;
+                    }
+
 					int localSheetID;
 					ExcelWorksheet nameWorksheet;
 					
diff --git a/EPPlus/ExcelWorksheet.cs b/EPPlus/ExcelWorksheet.cs
index ac1ff800..2a6e7e3d 100644
--- a/EPPlus/ExcelWorksheet.cs
+++ b/EPPlus/ExcelWorksheet.cs
@@ -185,13 +185,69 @@ public Formulas Clone()
         /// </summary>
         public class MergeCellsCollection : IEnumerable<string>
         {
-            internal MergeCellsCollection()
+            private struct AddressDimensions
             {
+                internal int StartRow;
 
+                internal int StartCol;
+
+                internal int EndRow;
+
+                internal int EndCol;
+
+                internal AddressDimensions(int startRow, int startCol, int endRow, int endCol)
+                {
+                    StartRow = startRow;
+                    StartCol = startCol;
+                    EndRow = endRow;
+                    EndCol = endCol;
+                }
+            }
+            
+            private readonly ExcelWorksheet _ws;
+            internal MergeCellsCollection(ExcelWorksheet ws)
+            {
+                _ws = ws;
             }
             internal CellStore<int> _cells = new CellStore<int>();
             List<string> _list = new List<string>();
             internal List<string> List { get { return _list; } }
+            
+            private IDictionary<string,AddressDimensions> _mergedAreasDimsCache = new Dictionary<string,AddressDimensions>();
+            
+            /// <summary>
+            /// Get MergeCell Index No
+            /// </summary>
+            /// <param name="row"></param>
+            /// <param name="column"></param>
+            /// <returns></returns>
+            public int GetId(int row, int column)
+            {
+                for (int i = 0; i < _list.Count; i++)
+                {
+                    var mergedAddress = _list[i];
+                    if(!string.IsNullOrEmpty( mergedAddress))
+                    {
+                        if (!_mergedAreasDimsCache.ContainsKey(mergedAddress))
+                        {
+                            ExcelCellBase.GetRowColFromAddress(mergedAddress, out var startRow, out var startColumn, out int toRow, out int toColumn);
+                            _mergedAreasDimsCache.Add(mergedAddress, new AddressDimensions(startRow, startColumn, toRow, toColumn));
+                        }
+                        
+                        var mergedDims = _mergedAreasDimsCache[mergedAddress];
+                        
+                        if (mergedDims.StartRow <= row && row <= mergedDims.EndRow)
+                        {
+                            if (mergedDims.StartCol <= column && column <= mergedDims.EndCol)
+                            {
+                                return i + 1;
+                            }
+                        }
+                    }
+                }
+                return 0;
+            }
+            
             public string this[int row, int column]
             {
                 get
@@ -226,6 +282,15 @@ internal void Add(ExcelAddressBase address, bool doValidate)
                 lock (this)
                 {
                     ix = _list.Count;
+                    var addressDimension = new AddressDimensions(address.Start.Row, address.Start.Column, address.End.Row, address.End.Column);
+                    if (!_mergedAreasDimsCache.ContainsKey(address.Address))
+                    {
+                        _mergedAreasDimsCache.Add(address.Address, addressDimension);
+                    }
+                    else
+                    {
+                        _mergedAreasDimsCache[address.Address] = addressDimension;
+                    }
                     _list.Add(address.Address);
                     SetIndex(address, ix);
                 }
@@ -324,29 +389,33 @@ System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator()
             #endregion
             internal void Clear(ExcelAddressBase Destination)
             {
-                var cse = new CellsStoreEnumerator<int>(_cells, Destination._fromRow, Destination._fromCol, Destination._toRow, Destination._toCol);
                 var used = new HashSet<int>();
-                while (cse.Next())
+                 _cells.Clear(Destination._fromRow, Destination._fromCol, Destination._toRow - Destination._fromRow + 1, Destination._toCol - Destination._fromCol + 1);
+                for (var row = Destination._fromRow; row <= Destination._toRow; row++)
                 {
-                    var v = cse.Value;
-                    if (!used.Contains(v) && _list[v] != null)
+                    for (var col = Destination._fromCol; col <= Destination._toCol; col++)
                     {
-                        var adr = new ExcelAddressBase(_list[v]);
-                        if (!(Destination.Collide(adr) == ExcelAddressBase.eAddressCollition.Inside || Destination.Collide(adr) == ExcelAddressBase.eAddressCollition.Equal))
+                        var mergedRangeId = GetId(row, col);
+                        
+                        if (mergedRangeId == 0 || used.Contains(mergedRangeId))
                         {
-                            throw (new InvalidOperationException(string.Format("Can't delete/overwrite merged cells. A range is partly merged with the another merged range. {0}", adr._address)));
+                            continue;
                         }
-                        used.Add(v);
-                    }
-                }
 
-                _cells.Clear(Destination._fromRow, Destination._fromCol, Destination._toRow - Destination._fromRow + 1, Destination._toCol - Destination._fromCol + 1);
-                foreach (var i in used)
-                {
-                    _list[i] = null;
+                        used.Add(mergedRangeId);
+                        // из метода GetId возвращается индекс в списке _list + 1, т.к. результат 0 означает, что значение в списке не найдено
+                        // поэтому, чтобы восстановить исходный индекс, передаем mergedRangeId-1
+                        var mergedRangeAddress = new ExcelAddressBase(_list[mergedRangeId-1]);
+                        if (Destination.Collide(mergedRangeAddress) == ExcelAddressBase.eAddressCollition.Partly)
+                        {
+                            throw (new InvalidOperationException(string.Format("Can't delete/overwrite merged cells. A range is partly merged with the another merged range. {0}", mergedRangeAddress._address)));
+                        }
+                        _list[mergedRangeId-1] = null;
+                    }
                 }
             }
         }
+        public bool DisableMergeValidation { get; set; }
         //internal CellStore<object> _values;
         //internal CellStore<string> _types;
         //internal CellStore<int> _styles;
@@ -396,6 +465,7 @@ public ExcelWorksheet(XmlNamespaceManager ns, ExcelPackage excelPackage, string
             _name = sheetName;
             _sheetID = sheetID;
             _positionID = positionID;
+            _mergedCells = new MergeCellsCollection(this);
             Hidden = hide;
 
             /**** Cellstore ****/
@@ -1664,7 +1734,7 @@ public ExcelRange SelectedRange
                 return new ExcelRange(this, View.SelectedRange);
             }
         }
-        MergeCellsCollection _mergedCells = new MergeCellsCollection();
+        MergeCellsCollection _mergedCells;
         /// <summary>
         /// Addresses to merged ranges
         /// </summary>
@@ -2524,8 +2594,27 @@ public void DeleteRow(int rowFrom, int rows)
             {
                 throw(new ArgumentException("Row out of range. Spans from 1 to " + ExcelPackage.MaxRows.ToString(CultureInfo.InvariantCulture)));
             }
+
             lock (this)
             {
+                var commentsDictionary = new List<ExcelComment>();
+
+                foreach (ExcelComment excelComment in Comments)
+                {
+                    var commentRow = Cells[excelComment.Reference].Start.Row;
+                    if (commentRow < rowFrom)
+                    {
+                        continue;
+                    }
+
+                    commentsDictionary.Add(excelComment);
+                }
+
+                foreach (var c in commentsDictionary)
+                {
+                    Comments.Remove(c);
+                }
+
                 _values.Delete(rowFrom, 0, rows, ExcelPackage.MaxColumns);
                 _formulas.Delete(rowFrom, 0, rows, ExcelPackage.MaxColumns);
                 _flags.Delete(rowFrom, 0, rows, ExcelPackage.MaxColumns);
@@ -2543,6 +2632,7 @@ public void DeleteRow(int rowFrom, int rows)
                 {
                     tbl.Address = tbl.Address.DeleteRow(rowFrom, rows);
                 }
+
                 foreach (var ptbl in PivotTables)
                 {
                     if (ptbl.Address.Start.Row > rowFrom + rows)
@@ -2550,6 +2640,7 @@ public void DeleteRow(int rowFrom, int rows)
                         ptbl.Address = ptbl.Address.DeleteRow(rowFrom, rows);
                     }
                 }
+
                 //Issue 15573
                 foreach (ExcelDataValidation dv in DataValidations)
                 {
@@ -2563,6 +2654,20 @@ public void DeleteRow(int rowFrom, int rows)
                         }
                     }
                 }
+
+                foreach (var commentToShift in commentsDictionary)
+                {
+                    var commentTarget = Cells[commentToShift.Range.Start.Row - rows, commentToShift.Range.Start.Column];
+                    var existingComment = commentTarget.Comment;
+                    if (existingComment != null)
+                    {
+                        existingComment.Text = commentToShift.Text;
+                    }
+                    else
+                    {
+                        commentTarget.AddComment(commentToShift.Text, commentToShift.Author);
+                    }
+                }
             }
         }
         /// <summary>
@@ -2863,22 +2968,7 @@ public void SetValue(string Address, object Value)
         /// <returns></returns>
         public int GetMergeCellId(int row, int column)
         {
-            for (int i = 0; i < _mergedCells.Count; i++)
-            {
-               if(!string.IsNullOrEmpty( _mergedCells[i]))
-               {
-                    ExcelRange range = Cells[_mergedCells[i]];
-
-                    if (range.Start.Row <= row && row <= range.End.Row)
-                    {
-                        if (range.Start.Column <= column && column <= range.End.Column)
-                        {
-                            return i + 1;
-                        }
-                    }
-                }
-            }
-            return 0;
+            return _mergedCells.GetId(row, column);
         }
 
 #endregion
diff --git a/EPPlus/ExcelWorksheets.cs b/EPPlus/ExcelWorksheets.cs
index 715d4693..82fbe0f6 100644
--- a/EPPlus/ExcelWorksheets.cs
+++ b/EPPlus/ExcelWorksheets.cs
@@ -153,7 +153,7 @@ public ExcelWorksheet Add(string Name)
             ExcelWorksheet worksheet = AddSheet(Name,false, null);
 			return worksheet;
 		}
-        private ExcelWorksheet AddSheet(string Name, bool isChart, eChartType? chartType, ExcelPivotTable pivotTableSource = null)
+        private ExcelWorksheet AddSheet(string Name, bool isChart, eChartType? chartType, ExcelPivotTable pivotTableSource = null, bool createVbaModule = false)
         {
             int sheetID;
             Uri uriWorksheet;
@@ -187,7 +187,7 @@ private ExcelWorksheet AddSheet(string Name, bool isChart, eChartType? chartType
                 }
 
                 _worksheets.Add(positionID, worksheet);
-                if (_pck.Workbook.VbaProject != null)
+                if (createVbaModule && _pck.Workbook.VbaProject != null)
                 {
                     var name = _pck.Workbook.VbaProject.GetModuleNameFromWorksheet(worksheet);
                     _pck.Workbook.VbaProject.Modules.Add(new ExcelVBAModule(worksheet.CodeNameChange) { Name = name, Code = "", Attributes = _pck.Workbook.VbaProject.GetDocumentAttributes(Name, "0{00020820-0000-0000-C000-000000000046}"), Type = eModuleType.Document, HelpContext = 0 });
@@ -202,7 +202,7 @@ private ExcelWorksheet AddSheet(string Name, bool isChart, eChartType? chartType
         /// </summary>
         /// <param name="Name">The name of the workbook</param>
         /// <param name="Copy">The worksheet to be copied</param>
-        public ExcelWorksheet Add(string Name, ExcelWorksheet Copy)
+        public ExcelWorksheet Add(string Name, ExcelWorksheet Copy, bool copyVba= false)
         {
             lock (_worksheets)
             {
@@ -268,7 +268,7 @@ public ExcelWorksheet Add(string Name, ExcelWorksheet Copy)
                 CloneCells(Copy, added);
 
                 //Copy the VBA code
-                if (_pck.Workbook.VbaProject != null)
+                if (copyVba && _pck.Workbook.VbaProject != null)
                 {
                     var name = _pck.Workbook.VbaProject.GetModuleNameFromWorksheet(added);
                     _pck.Workbook.VbaProject.Modules.Add(new ExcelVBAModule(added.CodeNameChange) { Name = name, Code = Copy.CodeModule.Code, Attributes = _pck.Workbook.VbaProject.GetDocumentAttributes(Name, "0{00020820-0000-0000-C000-000000000046}"), Type = eModuleType.Document, HelpContext = 0 });
diff --git a/EPPlus/Properties/AssemblyInfo.cs b/EPPlus/Properties/AssemblyInfo.cs
index b5c8c7fc..1c3c0588 100644
--- a/EPPlus/Properties/AssemblyInfo.cs
+++ b/EPPlus/Properties/AssemblyInfo.cs
@@ -46,7 +46,7 @@
 //
 //      Major Version
 //      Minor Version 
-//      Build Number
+//      Build NumberS
 //      Revision
 //
 // You can specify all the values or you can default the Revision and Build Numbers 
@@ -62,7 +62,7 @@
     //[assembly: AssemblyCulture("")]
     //[assembly: ComVisible(false)]
 
-    //[assembly: AssemblyVersion("4.5.0.0")]
-    //[assembly: AssemblyFileVersion("4.5.0.0")]
+    [assembly: AssemblyVersion("4.5.3.9")]
+    [assembly: AssemblyFileVersion("4.5.3.9")]
 #endif
 [assembly: AllowPartiallyTrustedCallers]
\ No newline at end of file