Notifications not Clearing from Notification Center

So this happens for all apps, but I'll use Facebook Messenger as my example.

I believe that in the past my notifications for an app would disappear from Notification Center after I viewed the relevant information in the app. So for example, let's say I have 10 notifications for the same conversation in FB Messenger showing up in N.C. - I then open the Messenger app and read the conversation. Next time I look at N.C. The notifications for that conversation should be gone.
Or let's say I have 10 emails notifications in N.C. and I open mail and open each email. When I open N.C. again those notifications should be gone.

So my problem is that this is no longer happening, for a few months now. On iOS 9 and it continues for me in the iOS 10 beta. Instead, even though I view the relevant things in each app, the notifications remain in N.C. and pile up until I physically delete them from there. Is this proper behavior? And if not how should I go about fixing this? Notification Center has gotten to be very overwhelming because of the mass pile ups that never delete on their own.

Thanks!