I made this thread public to let other users find the response and see the sample project.
The RadDocking control uses transparent WPF windows to display its ToolWindows by default and as a platform limitation of WPF, you cannot display any non-WPF content in such transparent windows. What you could do is to make the windows non-transparent by setting the RadWindowInteropHelper.AllowTransparency attached property of ToolWindow to False. This could be achieved using a custom GeneratedItemsFactory. Please refer to the attached sample project.
Hope this helps.
the Telerik team
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