Are you creating a EXE or DLL COM object?
If it is a DLL, are you building as a mutli-threaded DLL?

In my experience, I have found that Public variables share the same variables only across EXE COM object. If this is what you are to do, then EXE COM is the way to go. But, if this is the problem, then consister build the project to a MT DLL insteaded.