RaceOnRCWCleanup when closing WPF application with COM and "Enable unmanaged code debugging"

During development of my WPF application I suddenly got the seemingly much-dreaded RaceOnRCWCleanup when closing the application while debugging. When executing without debugger attached everything was normal.

Image and text of the warning message:

Managed Debugging Assistant 'RaceOnRCWCleanup' has detected a problem in 'MyEXE'. Additional Information: An attempt has been made to free an RCW that is in use. The RCW is in use on the active thread or another thread. Attempting to free an in-use RCW can cause corruption or data loss.

The stack trace was not very helpful:

   [External Code] 
>   mscoreei.dll!000007fef75c3309()     
    [Frames below may be incorrect and/or missing, no symbols loaded for mscoreei.dll]  
    mscoree.dll!000007fef7655b21()  
    kernel32.dll!0000000077b7f56d()     
    ntdll.dll!0000000077cb2cc1()    

Since the last bigger change I had made prior to the error occuring for the first time was using a COM object from my managed C# code I obviously suspected that OCX (written by me). Searching the net and stackoverflow did not yield any solution.

Then I found out that this only happens when the setting "Enable unmanaged code debugging" is activated. I had done that, because I wanted to debug my OCX written in unmanaged C++, too. Disabling unmanaged code d开发者_运维知识库ebugging made the problem go away immediately.

This happened on Windows 7, Visual Studio 2010 without SP1.

Does anyone have an explanation what is happening here? Is this a bug?

Update: This problem was gone when I installed service pack 1 for Visual Studio 2010.

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Not much to go by. However, do ignore this warning if you get it from terminating the debugging session early. It is caused by the MDA noticing a thread ending that has an outstanding COM interface call that's being marshaled. Using Debug + Stop Debugging can certainly trip this warning, it terminates threads.