If you go to http://gravatar.com/d6b10d5767d1e29006c11e1a2c590f3c (omit the /avatar/ from path) you get http://gravatar.com/clojita which seems to be your gravatar account, correct?
MD5 collision is unlikely (but maybe it’s time to buy a lottery ticket 🙂
Look at source fetches interesting detail — the comment in question has comment-author-clark class. So it’s not only the gravatar that is confused.
That class is generated in get_comment_class() function and is coming from user retrieved via $comment->user_id. It’s hard to guess more without hands on dumping of data, but my educated guess is that something is screwed up exotically in or around comment template.
First thing I’d try (dumping everything aside) is switching to native theme and/or looking into differences between theme’s comments implementation from original Underscores.