Usually after I've seen a new message and go back to the board, the thread no longer appears bold (unless there's more new posts on the next page) Just now, after reading post 13 of "Re: Outlander new episodes on demand?" in the TV Forum it still appeared bold when I went back to the board over and over again and took me back to post 13. I had to mark the Forum as read before the bold disappeared. Could it be that a moderator editing the post still had it open? The other forums worked normally.
@RogersRoland Like I said, I eventually marked it as read, so it's water under the bridge My theory is that the post was being read or edited by a mod at the time and not yet closed, so it kept coming up as new.