Actually, the PaneStateChanged also fires BEFORE
the docking is complete. So I've had to hack up a timer to delay removal of the extra SplitContainer for now. Not a great solution.
Here is my suggestion for what would be the correct fix. This would have to be done by Telerik since it is your implementation of Drag & Drop behavior:
On the DropEvent, check whether the ToolWindow's SplitContainer actually contains more than 1 PaneGroup.
- In the common case of a single group, move over only the Group and contents.
- Only in the case of multiple items in the SplitContainer, copy the SplitContainer as you are now.
This would facilitates reordering of singular PaneGroups within a SplitContainer without creating new SplitContainers.