Somewhere along the line, our good spoiler code got replaced with crap spoiler code. We can't hide things with it anymore.
Blame Cools! In all seriousness, my understanding is that the old spoiler plugin I used to use stopped being updated for compatibility with newer SMF versions. So Cools had to replace it.
I don't mind the new one too much except that it doesn't hide anything or indicate a spoiler when looking at a thread via Tapatalk. The old one said something like "<Spoiler for hiden>" [sic] when viewed via Tapatalk so that you at least knew someone used the spoiler tag on something.
That said, I think trying to hide this image for idol's sake wouldn't have really helped with the old plugin either. I'm pretty sure the content still loads; it's just collapsed.