With cross-wiki notifications, you get notifications from other wikis. However, as you move through several wikis for which there are no new notifications you may get pinged about the same notifications you already saw as if they were new.
I'll gave an example:
- I'm on English Wikipedia, and I got a notification from Commons. The badge turns blue and I can view there is a notification from Commons inside the cross-wiki notification bundle (which turns blue the first time I open it, and only the first time once T134854 is fixed). All this is great.
- When I go to Catalan Wikipedia, I see the notification badge highlighted in blue, but when I open it I found it is caused by the same Commons notification I have already seen. Since this is not new, I'd expect the notification no longer be considered unseen (at least when checked cross-wiki).
The proposal is to avoid highlighting a notifications from a different wiki if those have already been seen from any other wiki.