There’s a lovely unpatched “bug” to the OpenID plugin for WordPress. It seems to be directly related to logging in using an OpenID-associated email, when that email address wasn’t initially registered through WordPress as an OpenID (like the admin, upon setting up WordPress).
The worst bit about this bug, is how it fails entirely without a useful message. Usually it was something about formatting, like: “Catchable fatal error” of formatting.php on line 2829.”
I’ve fixed at least that much though.