Sometimes the lemmy frontend also changes the post that you're reading atm, but as far as we know it's not a security risk at the moment. It's just shown, you can't act as that user or post.

tl;dl: bug

Just websocket weirdness. Going away with version 0.18.

Oh wow. I've heard of comments ending up on the wrong thread, but that sounds bad.

edit: Come to think of it, I bet that has to do with why the vote counts vary so wildly sometimes (I just "upvoted" this post from 889 to 4)

Same, it was really strange, they were using a different theme as well, I thought I was tripping