You guessed it, it's another Rules update. Check here for more info

Tag changes for image #12546

Image		Tag	Action	Timestamp	User	Retained?
12546		+-SH horn Unwatch Watch Unspoiler Spoiler Unhide Hide Sign in to Watch Filter 12401	Added	6 days ago	Heat Sink Stop! This user is a staff member. Ask them before reverting their changes.	Yes