How to prevent User Roles from getting reapplied?
Try to run this: show tables like '%role%'; MySQL statement. In the results returned you should see a users_roles table (not users_role). To that table's columns are stored the uid and rid, therefore you will be able to find all users that have assigned with a role or more, and possibly an answer to your question.

I would kindly suggest you, since those roles are appeared again and again, to search any by chance or forgotten user_save implementation within your code.

Hope this help!