Going from past experience on another vBulletin forum......
I ended up having to unsubscribe/delete the topics I had already posted in to get the email notification to finally stop. I think it has some kind of memory if it was already enabled when you started posting.
Joe, I suspect what was posted should fix it for you.
Mav, did you change your usercp options that subscribe you to all threads? If it's not working as expected I'll work with you guys till we get it fixed.