The "new posts" icon is not disappearing for me in a consistent way.
If I open Classifieds, for example, it shows a dozen threads with new posts.
If I click the "mark read" button the page reloads, but the new posts icons are still there. If I force-reload the page, they disappear.
Same if I try to view one of the threads with new posts. For example if I go into off topic and click on the "new post" icon on the "what's bothering you" thread, I see the first new post (by beehatch). If I go back to off topic, the thread is still flagged as having new posts, and if I click the icon again I go to the same "new" post, even though I have already viewed it. If I force-reload the off topic index page, the icons disappear.
This is with Firefox on OSX.