Followers that say "unblock" instead of "block". How to delete them!?

More and more, I am being followed by random people (mostly spammers). If I try to block them, I can't because there is no "block" option with them, only an "unblock" option. Is this a hack? How do I get these people off my follower list? I've tried manually entering http://twitter.com/blocks/confirm/[username] and when I enter, it says blocked. But the user stays on my follower list, so I don't think it's successful. Thoughts?