even with "and receive email notifications of replies" turned off in preferences.
When you create a new thread I think by default the "watch & notify" are checked/enabled. So that could be the culprit.
Well I didn't get a notification for your reply on this thread (made after changing my preferences), but I did get a notification for a reply with an older thread (made prior to me changing my preferences),
so I guess it's keeping some old settings somewhere that isn't immediately obvious.