Posting a message marks the board as "unread" and the status is not changed when the board is visited.
At the moment I don't remember if it is intended or not (i.e. mark as read only when no more unread topics are present).
hmm... that seems to have stopped, now that I think about it, it may have been an issue with the file-based cache not invalidating the files properly.
What .. .file based you say :P
More than "fixed", something I won't care about... :P
Even though, if this is due to the cache, then we are going to be in troubles once hosting will start massively to use php... was it 5.5?