There may be some time lag .... wait a minute I'll check something ....
Hmmm, I'm not sure. Posts made in some forums don't increase post count, but it looks like most of yours were made in the Internet Marketing forum where they do count.
It might be a Bug. But as the forums are moving to Discourse soon I can almost assure you if there is it won't be getting fixed.
Any particular reason you're concerned about it? It's just a silly number, I never even pay any attention to mine.