Known bug that occurs when a 500-series error causes the database to not fully update, but a solution remains elusive. There are dozens of previous threads on this going back around a year, but they appear to have scrolled off the first page, so no reason for you to have known if you haven't run across it before.

The mods have requested that people NOT double post to fix it, or delete and repost, just wait for a natural response from somebody else to reset things. In the meantime, if you come across a wonky thread like this, you can view hidden replies by hitting the "Reply" button and scrolling down below the input box to view previous posts.