As I've mentioned before, I use the 'back' button on my browser to go back to the unread list and since we've had the extra adverts at the bottom of the forum, I have to press the back button three times to get it to work.
I think I've seen this happen in the past, although don't remember it being one particular forum. It didn't last very long and seemed to sort itself out; haven't seen it recently.
Perhaps try another browser (just as an experiment) and/or email the mods to see if anything's changed their end.