@caram and @willrax
Just had a quick play around with this and as far as I can tell, it appears to be working correctly for me, although is a little confusing e.g. difference between new topic and new post, unread count etc.
Clearing all your unread - at the bottom of the unread list (assuming you have some unread posts) there are two buttons - hover over and it will tell you what each does. One of them will basically mark all as read, once that has happened the content will refresh and change to a description of the default behaviour for unread as well as telling you that you can change that behaviour in your preferences.
The only slight bug I've noticed is that if I 'refresh' the forum by clicking on the "RubyMotion Community" Heading top left just under the RM logo and main menu bar, then the content of the forum updates, but not the menu bar, so the unread count did not refresh. It did refresh when I clicked on that menu option though.