No longer able to change screen brightness

After recent updates (within the past couple of days), I'm no longer able to set my screen brightness. Echoing numbers to /proc/acpi/video/VID/LCD0/brightness results in the value of that file being changed appropriately, as does plugging and unplugging my machine. However, the screen brightness never actually changes. I haven't found anything even remotely relevant in /var/log/{syslog,kern.log,acpid,dmesg}.

My system is a Lenovo ThinkPad R61i running Intrepid. I'm currently running kernel 2.6.27-11.27. I'm not certain I'm reporting this bug against the correct package. Of the recent updates, there are three possible candidates: gnome-power-manager is the least likely, since I'd think that twiddling /proc settings is at a lower level than g-p-m. Another candidate is acpi-support, but those updates came a bit too early, I think, and they didn't appear to have anything to do with the brightness setting. That leaves kernel updates which have been very frequent the last several days.

My symptoms are very similar to those described in bug 198476, but since that bug is fixed, and this is a recent regression, it's presumably not the same bug.

ProblemType: Bug
Architecture: i386
DistroRelease: Ubuntu 8.10
Package: linux-image-2.6.27-11-generic 2.6.27-11.27
ProcCmdLine: root=UUID=cf40ebf3-808f-4ab6-b7d9-52bf598a33b2 ro splash quiet
ProcEnviron:
 PATH=/home/username/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcVersionSignature: Ubuntu 2.6.27-11.27-generic
SourcePackage: linux