Visual Studio Crashes When Enabling Float or Document Mode on Custom Docked Panel During Design Time in .NET Core Projects

[NagarajManimaran]

Environment

Visual Studio professional 2026 - version 18.0.0

.NET version

Facing this issue in .NetCore

Did this work in a previous version of Visual Studio and/or previous .NET release?

No

Issue description

I am using a CustomDockingManager component to dock panels. After docking a panel, I set the EnableFloating property to true to make the panel float. However, Visual Studio crashes or becomes unresponsive during design time in .NET Core projects.
The same issue occurs when I try to set the panel to Document mode—Visual Studio crashes or hangs during design time.

I have attached a sample project (CustomFloatControl.zip) demonstrating the issue.

CustomFloatcontrol.zip

Kindly provide suggestions to resolve this problem.

Steps to reproduce

Open the sample project (CustomFloatControl.zip).
Drag and drop the CustomDockingManager component onto the form.
Drag and drop the CustomDockPanel control onto the CustomDockingManager.
Right-click the CustomDockPanel and set EnableDocking = true.
Right-click the CustomDockPanel and set EnableFloating = true.

Expected Behavior: The docked panel should float on the form without issues.
Observed Behavior: Visual Studio crashes or becomes unresponsive during design time.

Diagnostics

[KlausLoeffelmann]

The issue here is that you're doing the changes on the Form effectively only on the server-side of the WinForms Designer, which consists of 2 processes in .NET: The Client process is Visual Studio itself; it holds only Proxy Object of the actual controls. This is because Visual Studio itself is running in the Framework Process, but your controls in .NET. The actual visual representation of your controls is however done server-side, in a dedicated .NET process. Now. If you start to add and delete controls just in the server process, I assume just by looking at the code, the syncing of the Proxy Object -> Actual Control between client and server gets lost - and what you see happens.

Please take a look here, to ramp-up on how the mechanics behind this in the .NET WinForms Designer work.

https://devblogs.microsoft.com/dotnet/custom-controls-for-winforms-out-of-process-designer/

I have to say, though: The is not an easy scenario to implement, and the question is, if providing Design Time Support for this, is worth the effort.