- X writes a chat message addressed to me.
- Y writes a comment addressed to me.
- I visit the main site and read my inbox, which contains the notification of Y's comment.
- I haven't visited the chat since this started, so a chat message notification from X reaches my inbox.
- I visit the main site again and am notified of one message in my inbox. The order of the notifications is: Y's comment notification on top, then X's chat notification, then older notifications. So far so good; notifications are in chronological order according to the original event.
The bug is that the comment notification was highlighted as new, and the chat message notification wasn't. So the comment looked like a new comment (but it wasn't) and the chat message looked like something I'd seen (but I hadn't).
(Sorry, I didn't think of taking a screenshot. Devs: the two events were chat message and
comment. Now, of course, they both have
"IsNew":false; I don't know whether the
IsNew field was wrong then, or only the highlighting.)
Of course in real life it's often not just two items but a bunch of chat delayed notifications spread among a bunch of synchronous notifications. It gets rather messy.
This is a year-old bug (at least) that the new top bar didn't fix.
Given the existence of delayed notifications, either inbox elements can be in event chronological order (as opposed to delivery chronological order), or the new items in the inbox can always be the top ones. But it can't be both.