Cannot login when shutdown command is overtaken by XUbuntu log-out

[Ivo Peterka]

XUbuntu 11.10
LightDM 1.0.6-0ubuntu1.6

Steps to reproduce:
1. In standard XUbuntu installation bring up the terminal, type "sudo shutdown -P +80" and press enter. Don't fill in password.
2. Choose Log-Out screen from XUbuntu system menu and turn off computer using this GUI possibility to do it (leaving the terminal with shutdown command opened).
3. Start the computer - the LightDM will not let you log-in as common user, because the system identifies itself as in shutdown mode and the only user that can log-in is root, which can be tricky in Ubuntu as sudoers does not need to set root password.