Sometimes and only sometimes when I have come to read posts and there are a lot of them, especially on the threads that I am interested in when I go back to the main thread board all of the have not read markers are cleared. This has happened quite a few times although it does not happen all the time. It only seems to happen when I spend several minutes catching up on a thread with a lot of new posts.
It's not really a bug, it's just the way the system has been constructed. When you first visit the site, a "cookie" (small text file) is sent to your browser that lasts for about 20 minutes. As soon as the 20 minutes is up, the cookie expires, which tells our system to remove all of the current "new post" icons. The problem is that if you haven't finished reading all of the new posts before the 20 minutes is up, everything will get reset and you won't know which posts are still unread. The problem is the 20 minute time frame. If you extend it, the new post icons won't update fast enough for those that visit the boards often for only a few minutes at a time. If you shorten it, then the icons disappear before you have a chance to read everything. The only way that the system could ever be perfectly accurate is if the "20 minute system" was trashed and each person consistenly logged in to view the boards and then - more importantly - logged out upon finishing. However, nobody likes to log in and out everytime they view a site, which brings the whole situation back to square one.