I've also never watched a short, or if I did I immediately removed it from my watch history. I do keep that trimmed with prejudice, because the algorithm is desperate to show me something other than what I normally watch.
Why it happens with remove-animations: well I'm pretty confident they don't test with it. But it's super freakin' weird. I kinda doubt it'll get fixed though, doing so will cause "engagement" to drop, and it has been happening for most of a year now.