Its something to do with the way the forum runs its clean ups......
When the forum runs its database backups it corrects the post counts (why these are supposedly wrong, I do not know
) maybe that the post count was changed at some point (which can be done in our control panel) and the forum has corrected the count to the actual figure posted..
Will always change as posts are removed but as pointed out it would only be the odd post here and there........
Hope this helps.......