If I remember correctly, this occurred a site which just switched to the new notification menu. Are you saying that the dismissals are scoped to the selected tab? It never even occurred to me to try that. I rarely have more than a few notifications, so I haven’t had much reason to use the tabs.
Personally I like Sam’s suggestion (much cleaner than mine). That said, this was a very light suggestion anyway since I also rarely have “important” notifications. Just figured I’d bring it up since I ran into it.
Slight tangent, but I personally would find more use in being able to dismiss individual notifications, similar to a feature Facebook has. Should I open a new topic for that?