I was going through the mod panel and I saw this:
It's an answer that's been deleted already. I thought that flags were handled automatically after deletion? Should this be fixed?
There is sometimes a race between users adding flags, and moderators wiping them out. Sometimes, this has resulted in a "not an answer" (etc) being added to a post that has actually just been deleted (note: it isn't a problem the other way around). In addition to leaving "false positives" for moderators, it can (based on evidence) also mean that 10k users are adding additional flags to a deleted post (in one case, 4 extra flags after deletion).
To stop this creating unnecessary work for everyone, from the next build only bespoke flag-for-moderator-attention flags will be accepted on deleted posts; otherwise, it'll just politely tell you that the post is now deleted. This still retains the ability to flag a deleted post for something out of the ordinary (undeletion, even-more-aggressive deletion, etc).
When a moderator closes or deletes a flagged post, pending flags on this post are cleared. There are two cases where you might see a flag on a deleted post.
Note that it should still be possible to flag deleted posts to contact a moderator (for example to request undeletion).