This problem can nicely produced with the MDITabs demo. If you select standard MDITabs and select a different window tab that will the active close button under your mouse, the window will close. So in a sense all that you are trying to do is select a new tab, but the MouseMove in the CMFCBaseTabCtrl does not care and sets the tabclosebuttonpressed flag the mouse up then closes the mdi window.
Visual Studio/Silverlight/Tooling version
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