You can disable automatic subscriptions in your user cp
here under 'edit subscription mode.' That will help a bit.
Are you unsubscribing like this?
- click the checkbox next to the threads that you'd like to remove
- choose "delete subscriptions" from the drop down menu
- click "go"
That removes my subscribed threads.
Let me know if you're still having problems after trying that, and we'll see what we can do.