Expose API that allows you to easily customize the title bar buttons. 

 Improve resizing behavior when RadWindowInteropHelper.AllowTransparency attached property is set to True

If you have your windows taskbar set to auto hide it won't show when you move your cursor to the edge of the screen when a TabbedWindow is maximized.
Is there a workaround for this or is this a bug that you will fix?

Currently, if you create a control that derives from RadTabbedWindow and then drag out a tab to create a new window, the newly created window is of type RadTabbedWindow. This feature will be useful if you want the newly created window to be the same type as the custom window that initializes the new window creation.

Make it possible to create windows of a custom type when dragging a tab out of the control.

It would be great if there is an easy way to add some custom content after the tab items. Currently, this functionality can be achieved by modifying the template.

TabbedWindow with 2 tabs, each tab has Frame which almost fully covers the content.

Step 1) Drag drop a tab to the visible content. 2) Then bring it back to the first window with drag drop. Step 1 is now impossible - no window is created after drag out of tab strip and drop onto the content.

Possible workaround: Set AllowDrop to True to the control (in this case frame) in the content of the RadTabItems.

Click and move a control which is hosted in the Content of the RadTabItem starts dragging of the tab which is unexpected.