I've had problems off and on with the unread posts button showing all of the unread posts. Sometimes I get them all, but sometimes afterwards when I go to the Home page, I notice there are more new posts to read that "show unread..." didn't show.
So, no, it isn't just you, Murrelet... but I've never run into the problem of it not showing any of the new posts. Just some of them. Haven't quite figured out which the program chooses.
-dayle