Not sure if that's a bug or a feature, but I'll share it with you:
I still have some unread notifications, however, the counter at my avatar vanished.
I would have expected it to show me thenumber of unread notificationsI have.
It could be feature, to only display "new" notifications (since my last visit to the notifications-area); when I started today, I had the counter on 5, then I visited my Notifications. I read some of them, but not all.
it's indeed not a bug, but a feature. The change is on purpose to show only the new notifications in the header and when you enter your notifications, that number is wiped until you have new notifications.
The plan is to add a number in the notification stream itself to show you the unread messages.
You can read up on a explanation by Sajid here: Follow the yellow brick road...