Comment 11 for bug 718670

According to a Fedora bug report, see below, exporting the `superusers` variable seems to fix it.

Concretely, all you need to do in your custom `01_users` script is:
set superusers="root"
export superusers
password_pbkdf2 root ...

I've tested it on Ubuntu 12.04 LTS (with the latest updates as the date of this comment).