Comment 7 for bug 844241

Adding lightdm because I've discovered another issue:
1)boot Ubuntu
2)leave pc idle without logging in
3)after 10 minutes (as I've set in screen settings) the screen goes standby
4)I cannot restore backlight even using keyboard shortcut (I think because I'm not logged in)
5)I've only one user so the focus is on password field, so I can enter the password although the screen is off
6)As soon the system enter Gnome session I can restore backlight using keyboard shortcut

Is a strange problem...maybe it affects more modules (ligthdm, gnome-power-manager, graphic card driver??...), but I cannot reproduce it on other laptops, does anyone have a tip on how to isolate this bug to help resolving it?

Thanks