Browser tab shows unread count but nothing is unread

I think this happens if you have multiple tabs open to the same Pleroma instance, but I'm not sure.

The symptom is that the tab title says something like (2) bikeshed.party but there's no unread notifications and the timeline you're viewing has no new messages to read.

My suspicion is that I marked notifications as read in another tab which was somehow synced to the other tab's Pleroma instance but that tab's title was not updated.

Open to other theories about how this is happening.