The object is always deleted by the same library that created the shared_ptr. This is done by instantiating an appropriate deleter at construction time. You can defeat this by creating the object in library A and the shared_ptr in library B, of course.

Mixing single- and multithreaded libraries might be a problem for other reasons, but even that should work on Windows with Boost 1.33 with the default configuration.

Thanks Peter, please disregard my reply to your other email.