MAL's option to flag a series as "rewatching" is broken. Whenever I click the little + button to update the number of episodes I've watched, it adds entries in my history for the entire rest of the series as well as that episode.

It's even more broken in combination with the recent anime dynamic images. The faulty entries show up in there but then don't get removed when I delete them from my history until I update my list with a new episode. Well, I found a way to fix that, at least. If you set the signature image type to Custom - Recent Anime Updates and then choose Split rows by individual ep/chapters (this option disappears when the type isn't set to a custom one but it still affects the other types), then switch the type back to Recent Anime Updates you can then force it to update the image by clicking the Update Signature button.

The site's easy to use and I really like all the little AJAX features, it just seems that some features are completely half-assed.