Steps to reproduce:
1) Create a topic with single post.
2) Note the board stats about total posts/topics.
3) Permanently delete the post from viewtopic (the topic will be deleted too).
4) Check the board total topics/posts stats - board total posts count isn't decremented.

This may lead to cases like Total posts: 1 :: Total topics: 0.
The only way to fix for now is resyncing stats from ACP.
Also, it seems to be braking the forum stats.