When a user that's on moderation queue edits one of his approved posts, it's not marked as unapproved as was the case in 3.0. This is likely a bug introduced by soft-delete. I assume that this is not the intended behaviour for 3.1 as the "This message has been edited successfully, but it will need to be approved by a moderator before it is publicly viewable. You will be notified when your post has been approved." message is still presented to the user.