Vista - Bug (undocumented feature?) in Credential Provider subsystem

Has anyone here tried to write a custom Authentication Package and
Credential Provider on Vista? I'm trying to do this, but I've
encountered a bug (or an undocumented feature) in the Credential
Provider subsystem.

I can successfully log into an interactive session, but it seems that
the credential provider subsystem is trying to read my custom
authentication package's profile buffer. I don't place any meaningful
data in there, and the Authentication Package specs don't require me
to.

The credential provider subsystem randomly crashes depending on what
kind of data the auth package returns. And, when it doesn't crash, a
bubble appears in the task bar telling me that my user's account is
about to expire. My auth package works just fine on XP. It only does
this on Vista.

If any Microsoft dev people could help me find a workaround, it'd be
appreciated.

--
Peter Rutenbar