Tell HN: Up/downvotes of comments on HN are silently ignored when using Tor

I noticed that whenever I upvote or downvote a comment while connected through Tor, my vote is silently ignored. I still get the "unvote/undown" button, but the user karma in their profile remains unchanged. I can repeat the same while connected through the clearnet, and everything works as expected: The karma of the affected user changes accordingly. The upvotes for the stories work fine though.

Is this a new defense from bots? Why does it affect established user accounts like mine? Has anybody else also noticed this?