Me too. I got notified about posts in 2 subscriptions that I have since unsubscribed, and I still can't clear the notifications.Same problem. Also, notifications (I mean that little thing that says you have a subscription on each page you view, on the top) aren't clearing when I click through.
Which leads me to a second problem: I'm occasionally getting subscribed to threads that I only posted in, and did not actively subscribe to. The 2 notifications mentioned above were like this. I have gotten a third subscription of this kind...but, despit a new post, it hasn't generated a notification...yet. (I expect one later.)