[i945gm] LCD backlight won't stay off

Binary package hint: xorg

Currently on lucid beta, also experienced this on karmic for sure and possibly earlier.

Gnome's screensaver is off, and power management is set to turn off the monitor after ten minutes.

"xset dpms force off" turns off the screen and backlight for approximately a minute, before the display turns back on. Seemingly randomly, the 10 minute timer only blanks the screen rather than also turning off the backlight. This occurs under metacity and compiz.

This is a single lcd on an intel-video laptop; I also see seemingly identical symptom on two desktops with nvidia video cards running dual-head desktops under both metacity and compiz (proprietary driver, under karmic and jaunty), and on a singleheaded radeon 9250 (open driver, karmic), (1) where the display's may be sit for days without turning off the backlight despite the power options being configured, (2) "xset dpms force off" turning the backlight off, and then back on to a full display after a minute or so.

ProblemType: Bug
Architecture: i386
Date: Mon Dec 28 07:33:35 2009
DistroRelease: Ubuntu 10.04
InstallationMedia: Ubuntu 10.04 "Lucid Lynx" - Alpha i386 (20091209)
MachineType: Acer Aspire 3690
Package: xorg 1:7.5~3ubuntu4
PccardctlIdent:
 Socket 0:
   no product info available
PccardctlStatus:
 Socket 0:
   no card
ProcCmdLine: BOOT_IMAGE=//vmlinuz-2.6.32-9-generic root=/dev/sda6 ro crashkernel=384M-2G:64M,2G-:128M quiet splash
ProcEnviron:
 PATH=(custom, user)
 LANG=en_CA.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.32-9.13-generic
RelatedPackageVersions:
 xserver-xorg 1:7.5~3ubuntu4
 libgl1-mesa-glx 7.6.1~rc3-1ubuntu1
 libdrm2 2.4.14-1ubuntu2
 xserver-xorg-video-intel 2:2.9.1-1ubuntu1
 xserver-xorg-video-ati 1:6.12.99+git20091125.0061c4db-0ubuntu1
SourcePackage: xorg
Tags: lucid
Uname: Linux 2.6.32-9-generic i686
XorgConf: Error: [Errno 2] No such file or directory: '/etc/X11/xorg.conf'
dmi.bios.date: 02/13/2007
dmi.bios.vendor: Acer
dmi.bios.version: V3.50
dmi.board.name: Grapevine
dmi.board.vendor: Acer
dmi.board.version: N/A
dmi.chassis.type: 10
dmi.chassis.vendor: Acer
dmi.chassis.version: N/A
dmi.modalias: dmi:bvnAcer:bvrV3.50:bd02/13/2007:svnAcer:pnAspire3690:pvrV3.50:rvnAcer:rnGrapevine:rvrN/A:cvnAcer:ct10:cvrN/A:
dmi.product.name: Aspire 3690
dmi.product.version: V3.50
dmi.sys.vendor: Acer
fglrx: Not loaded
glxinfo: Error: [Errno 2] No such file or directory
system:
 distro: Ubuntu
 architecture: i686kernel: 2.6.32-9-generic