Not sure I understand your question. It's a plain race condition between your worker thread and the rest of the system.
What happens is that your queue will continue to process data (even if it's just your quit-command) while the rest of the system assumes your module is all done and can be destructed. If module manages to destroy some variables in your module before your worker thread is done, chances are you'll see the error. If you get this type of error, it means that something was still running while it shouldn't be. You should never expect to see this type of error if your threading is done correctly.
