diff --git a/app/code/core/Mage/Core/Block/Abstract.php b/app/code/core/Mage/Core/Block/Abstract.php
index adf82c0834a..f1b433066bf 100644
--- a/app/code/core/Mage/Core/Block/Abstract.php
+++ b/app/code/core/Mage/Core/Block/Abstract.php
@@ -464,6 +464,7 @@ public function setChild($alias, $block)
 
         $block->setParentBlock($this);
         $block->setBlockAlias($alias);
+        $this->unsetChild($alias);
         $this->_children[$alias] = $block;
         return $this;
     }
@@ -482,7 +483,7 @@ public function unsetChild($alias)
             unset($this->_children[$alias]);
             $key = array_search($name, $this->_sortedChildren);
             if ($key !== false) {
-                unset($this->_sortedChildren[$key]);
+                array_splice($this->_sortedChildren, $key, 1);
             }
         }
 
@@ -741,7 +742,6 @@ public function insert($block, $siblingName = '', $after = false, $alias = '')
      */
     public function sortChildren($force = false)
     {
-        $this->_sortedChildren = array_values($this->_sortedChildren); // reset indexes which might have gaps after unsetting blocks
         foreach ($this->_sortInstructions as $name => $list) {
             list($siblingName, $after, $exists) = $list;
             if ($exists && !$force) {
diff --git a/tests/unit/Mage/Core/Block/Text/ListTest.php b/tests/unit/Mage/Core/Block/Text/ListTest.php
new file mode 100644
index 00000000000..e46f856e4f6
--- /dev/null
+++ b/tests/unit/Mage/Core/Block/Text/ListTest.php
@@ -0,0 +1,103 @@
+<?php
+
+/**
+ * OpenMage
+ *
+ * This source file is subject to the Open Software License (OSL 3.0)
+ * that is bundled with this package in the file LICENSE.txt.
+ * It is also available at https://opensource.org/license/osl-3-0-php
+ *
+ * @category   OpenMage
+ * @package    OpenMage_Tests
+ * @copyright  Copyright (c) 2024 The OpenMage Contributors (https://www.openmage.org)
+ * @license    https://opensource.org/licenses/osl-3.0.php  Open Software License (OSL 3.0)
+ */
+
+declare(strict_types=1);
+
+namespace OpenMage\Tests\Unit\Mage\Core\Block\Text;
+
+use Mage;
+use PHPUnit\Framework\TestCase;
+
+class ListTest extends TestCase
+{
+    public function setUp(): void
+    {
+        Mage::app();
+    }
+
+    /**
+     * @group Mage_Core
+     * @group Mage_Core_Block
+     */
+    public function testDuplicateBlockName(): void
+    {
+        $layout = Mage::getModel('core/layout');
+
+        $parentBlock = $layout->createBlock('core/text_list', 'parent');
+
+        $childBlockA = $layout->createBlock('core/text', 'child_a')->setText('A1');
+        $parentBlock->append($childBlockA);
+
+        $childBlockA = $layout->createBlock('core/text', 'child_a')->setText('A2');
+        $parentBlock->append($childBlockA);
+
+        $this->assertSame('A2', $parentBlock->toHtml());
+    }
+
+    /**
+     * @group Mage_Core
+     * @group Mage_Core_Block
+     */
+    public function testDuplicateBlockNameOrdering(): void
+    {
+        $layout = Mage::getModel('core/layout');
+
+        $parentBlock = $layout->createBlock('core/text_list', 'parent');
+
+        $childBlockA = $layout->createBlock('core/text', 'child_a')->setText('A');
+        $parentBlock->append($childBlockA);
+
+        $childBlockB = $layout->createBlock('core/text', 'child_b')->setText('B');
+        $parentBlock->append($childBlockB);
+
+        $childBlockC = $layout->createBlock('core/text', 'child_c')->setText('C');
+        $parentBlock->append($childBlockC);
+
+        $parentBlock->unsetChild('child_b');
+
+        $childBlockB = $layout->createBlock('core/text', 'child_b')->setText('B');
+        $parentBlock->insert($childBlockB, 'child_c', false);
+
+        $this->assertSame('ABC', $parentBlock->toHtml());
+    }
+
+    /**
+     * @group Mage_Core
+     * @group Mage_Core_Block
+     */
+    public function testUniqueBlockNameOrdering(): void
+    {
+        $layout = Mage::getModel('core/layout');
+
+        $parentBlock = $layout->createBlock('core/text_list', 'parent');
+
+        $childBlockD = $layout->createBlock('core/text', 'child_d')->setText('D');
+        $parentBlock->insert($childBlockD, 'child_c', true);
+
+        $childBlockC = $layout->createBlock('core/text', 'child_c')->setText('C');
+        $parentBlock->insert($childBlockC, 'child_b', true);
+
+        $childBlockA = $layout->createBlock('core/text', 'child_a')->setText('A');
+        $parentBlock->insert($childBlockC, 'child_b', false);
+
+        $childBlockB = $layout->createBlock('core/text', 'child_b')->setText('B');
+        $parentBlock->insert($childBlockC, 'child_a', true);
+
+        $parentBlock->unsetChild('child_a');
+        $parentBlock->unsetChild('child_b');
+
+        $this->assertSame('CD', $parentBlock->toHtml());
+    }
+}