This is really quite unfortunate. I would say it's a bit rude to downvote posts from communities you're not a member of. Really shouldn't users be blocking the community from appearing in their feed?
I may take this up with the Lemmy developers. I think only being able to vote on posts in communities you're subscribed to would be an improvement. Wouldn't it?
Oh, that's perfect. Thanks for letting me know! Will grit my teeth until then! 😬