Comment 7 for bug 444067

Chris, you're right. The correct steps to reproduce the bug are:
# adduser foobar
# usermod -G adm,disk,dialout,cdrom,plugdev,lpadmin,admin,sambashare,mythtv -a foobar
Eventually you need to remove some of these groups on your system.

Michał, can you post the output you get when running "groups" in a terminal?