The canned DllMain for MFC 8.0 does not seem to call ExitInstance when it gets a DLL_PROCESS_DETACH. One possible solution is to define my own DllMain, but how do I tell the linker to use mine and not MFC's?
Or, is there another override which gets called on DLL_PROCESS_DETACH I'm not aware of?
I have had similar issues for a project compiled with /clr. Are you in the same situation? I was never able to trace it to a specific condition, but changing some static initializers to set null cleared it up. I think it has something to do with the order that static destructors are registered.
I'm not sure why your ExitInstance isn't called, but it's possible to define your own DllMain by copying the contents of MFC's dllmodul.cpp file into a file in your dll and adding any extra required functionality. The procedure is documented in this MS knowledge base article. Though it was written for MFC 4.0, I have used this method successfully for apps using MFC 8.0.