Recently I was sent a notification about the ability to set room guidelines. However, while this shows in the inbox, it seems to be counted wrong. If the notification is unread, then the red number is 0. If the notification is read, then the red number is -1.
This isn't Inbox indicator shows negative counter as that question was caused by a deleted comment. This doesn't go away on reload, and I can easily set it back and forth. My bug report is not about a race condition where the source of a notification is deleted while the inbox is open. Instead, this bug report is about a specific notification which links to a specific, undeleted post. There's a longer discussion about dupe-ness in the Teachers' Lounge (mod-only link).

