I can't find the thread where I posted pictures showing what we were describing here.... but I wanted to point out that the forum I used in the example has just switched over to the same forum software that we're using here, and they have it working... so it must be possible
To recap:
On this forum, if you click "whats new" or "new posts" and read one of the threads, and then click "whats new" or "new posts" again, the thread does not show up.
On other forums, if you click "whats new" or "new posts" and read one of the threads, and then click "whats new" or "new posts" again, the thread is still in the list in chronological order, but it goes from being bold font to regular font indicating that there hasn't been any changes in the thread since you last read it.
Here's the reference i'm using: http://184.172.224.209/~wwwfulls/for...archid=1695654