Sometimes I read a PM and then choose “defer” to mark it unread again, to indicate that I have to look at this PM later. Before the update when we got the sidebar, choosing “defer” would give me a circle with the number 1 on my avatar to indicate that I have an unread PM. And when clicking on my avatar, the unread PM would show up in the list.
If I read a PM now, and choose “defer” to mark it unread, the PM icon doesn’t reappear on my avatar, and the PM doesn’t show up in the notifications. (But it shows up as unread in my inbox.)
Truly unread PM:
After reading it and choosing “defer”:
I hope this is a bug that can (and will be fixed), and not an intentional change.