I'm fairly sure there are multiple downvote bots operating on HN. Frequently, certain comments to topics considered by some as "political" on HN will get an immediate 2 or 3 downvotes in the first 30 seconds, and then over the course of the next 2 or 3 hours, be upvoted back up to black.

Although it's possible that there's some confounding happening here, such as the handful of people who hit refresh on HN hundreds of times a day are also ones who can't stand certain political viewpoints. But it seems unlikely. Far more likely is that there are a handful of downvote bots in operation on a keyword basis.

It's not a huge deal to me, but it does seem kind of obvious.