I've already seen the notification.
WHY U NO GO AWAY!?
not sure it was there at the beginning, but there is now a "Mark all as read" button at the top of notifications.
So the problem is solved now. When you have new alerts there is a button that appears to the top right of the notification page, labeled "Mark all as read". Click that and the notifications clear up.
correction: it does go away but you have to press F5
Yep! They'll go away upon refreshing the page. Unfortunately we can't do anything about the notifications feature, the defaults, etc.. That's all part of the site provider's build. They're always updating things though so hopefully this is something that gets updated over time.