Here's a thing I do a lot:
- Get a toast about a PM, and an inbox message.
- Click it, interact with the PM.
- See my inbox lit up.
- Visit it, see the notification about the PM I'm already in, click it to visit that PM and close one or the other tab.
That notification should probably just vanish when I visit the PM itself!
(I don't like using "clear all notifications" since I could click it with bad timing and wipe out a notification I don't see there.)