Has anyone else this problem?

When I want to upvote a story, my vote is not accepted:

The upvote arrow disappears (as usual), but the vote counter stays exactly the same when the page is refreshed.

This happens both when I try to upvote something on the comments page and on the front page (list).

Why? Why am I being blocked like this? I didn't do anything wrong and my "karma" is currently at 1359.

If this is HN's idea of "democracy", then I'm definitely out of here.

Please let me know what this is all about.

Thanks.