I push the "unread posts" tab, and it shows no unread posts. But if I click on the "recent topics" tab, I see that there have been several posts that I have not seen...
As I have understood it, it might be normal. It actually leads you to the "Unread posts since last visit" page and that one is cleared of unread posts everytime you log out. But there is a line on that page saying "No unread topics found since your last visit.
Click here to try all unread topics", and if you go ahead and click that link I think you'll find what you're looking for.
I guess "Unread Posts" is a bit misleading. I've actually never even noticed those links before! Were they there in the old theme also?