On my end everything seems to be there, the "new posts" that you have not viewed are in bold and the ones you have read are in regular font. And then posts that have been read since your last log in are in a "separate" location which reads "Threads below have not been updated since your last visit".
Everything works great, nothing vanishes from the NEW POSTS page on my end. You have posts you have not seen (in bold), you have posts you have seen in regular font, and you have posts that haven't changed since last log in. I mean that covers everything does it not? So yeah it is awesome, I don't see any issues at all.
The "threads don’t vanish but they vanish from the new posts page until there is another new post" doesn't seem to apply, I mean I can see everything. But maybe I am just a moron and am not understanding what you are saying.
