I've observed this issue with acpid/acpi-support, gnome-power-manager and xfce4-power-manager in Ubuntu 11.04 and Xubuntu 11.04 and 11.10, so I'm thinking that it might be an xorg issue. After running 'xset dpms force off' with lid closed on a laptop to disable the backlight, moving the mouse or touching the keyboard will cause the backlight to turn back on. The backlight should never turn on under any circumstances when the lid is closed, unless maybe in the case that the user runs 'xset dpms force on' explicitly. Corresponding Ubuntu bug report is here: https://bugs.launchpad.net/ubuntu/+source/x11-xserver-utils/+bug/41994
This is not a bug with xset, moving to server component. Sounds more like an ACPI bug to me, but I'm not very familiar with that side of the fence.
Mass closure: This bug has been untouched for more than six years, and is not obviously still valid. Please file a new report if you continue to experience issues with a current server.
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