One way to reproduce this (occasionally) is as follows:
1. Create a docking layout in the designer that has a ToolTabStrip, for docking tool windows.
2. At run-time, dock 3 tool windows into this ToolTabStrip
3. Set docking for the 3 docked tool windows in the ToolTabStrip to "float"
4. Set docking for the 3 previously docked (then floated) tool windows to "hidden"
5. Wait a little while (a few minutes?)
6. Try to re-dock one of the the previously docked/floated/hidden tool windows into the ToolTabStrip
7. The ToolTabStrip.Collapsed property is set to false (as viewed using the debugger) and the attempt to re-dock the tool window in step 5 gives the exception "Changing children collection of an already disposed element" .
Unfortunately, the exception doesn't always happen. I repeated the above process 3 times and the exception happened once.