There are some little things like this that we have noticed. They actually were noticed back when the site was in beta (prior to public release) but as we still (after more than a year in public use) have not figured out exactly what causes this, we are stumped.
Some things we can explain, like you might get a message that a topic you are watching has a new post and when you check by clicking you get a "can't find topic" message. That is because the post that triggered the message either has been deleted or edited. When a post is edited by the individual who posted it, the original post number disappears and a new post number is assigned.
One of the most aggravating things to me, both as a user and a moderator, is when a topic I am "Watching" all of a sudden stops being watched by me?? I have had it happen to topics I started. :?
In any case, we are still trying to figure out the reasons.
