Odd. From what I can see, the most recent post you've made thats been deleted was just over 2 months ago, and you deleted it yourself. Admin could have set a sub-forum to not contribute to postcount, but I'm not sure why Tran would have. Thats normally done to combat postwhoring, and we haven't had problems with that in a very long time. Even less likely is a few threads that you've heavily participated in a long time ago (but not recently) got deleted.
Are you aware of any particular threads that you've made dozens of posts in? I could check those to see if anything has changed with them.