Let me show you by screenshots.
My "threads I'm on" pages shows 30 replies on the top thread (troll knickers thread).
When I log in, it says there are only 28 posts.
I logged in and out a few times and it didn't change anything to make the numbers agree.
A night watchmen posted a few times, so I'm wondering if that just isn't counted in the numbers, or is there a glitch?