Yeah, it's a current bug. The feature was working before and I think it's an easy fix so it should be back to normal in the next update or two.~~
EDIT: Scratch that, it seems to be working fine. I'll have to check this out in more detail.
EDIT2: Are you possibly trying to hide a sticky post? Because currently you can hide it but then it comes right when you refresh the feed.
EDIT 3: Ah, so if you hide any post, it will hide it but it doesn't seem to be saved because once you refresh the feed, the post that should be hidden is back.