strange behaviour for notifications

maybe it's something to do with instance-specific race conditions, but old notifications keep reappearing as new after having been previously marked "Read". no idea what information might be helpful here (and maybe this is really something to do with the backend?), but one thing i've noticed, though, that seems a bit reproduce-able:

1. open web client and log in
2. notification sidebar has nothing, or maybe one thing, in it
3. load own timeline, which contains a that was directed at me and that i've repeated
4. that post appears in the notifications sidebar as "unread"