Brightness control keys stopped working after latest 12.04 post beta1 update

[Alex]

I'm using a new Toshiba Portege Z830.

Brightness control keys on my laptop (Fn+F6 and Fn+F7) are working when booting the 12.04 beta1 ISO image. They still work after installing beta1 without the updates on the hard drive.

However, after applying the latest updates from the network, the brightness controls are not working anymore.

There is a correct keypress event (not sure if it's normal that it appears 4 times for each keypress though):
$ xev | sed -n 's/^.*state \([0-9].*\), keycode *\([0-9]\+\) *\(.*\), .*$/keycode \2 = \3, state = \1/p'
keycode 232 = (keysym 0x1008ff03, XF86MonBrightnessDown), state = 0x10
keycode 232 = (keysym 0x1008ff03, XF86MonBrightnessDown), state = 0x10
keycode 232 = (keysym 0x1008ff03, XF86MonBrightnessDown), state = 0x10
keycode 232 = (keysym 0x1008ff03, XF86MonBrightnessDown), state = 0x10
keycode 233 = (keysym 0x1008ff02, XF86MonBrightnessUp), state = 0x10
keycode 233 = (keysym 0x1008ff02, XF86MonBrightnessUp), state = 0x10
keycode 233 = (keysym 0x1008ff02, XF86MonBrightnessUp), state = 0x10
keycode 233 = (keysym 0x1008ff02, XF86MonBrightnessUp), state = 0x10

And an ACPI event is generated:
$ sudo acpi_listen
video DD01 00000087 00000000
video DD01 00000086 00000000

However, there is no scancode generated in keymap:
$ sudo /lib/udev/findkeyboards
AT keyboard: input/event3
$ sudo /lib/udev/keymap -i input/event3
Press ESC to finish, or Control-C if this device is not your primary keyboard

Finally, the following line appears on each keypress in /var/log/kern.log:
Mar 7 21:01:53 portege kernel: [ 636.342659] ACPI: Failed to switch the brightness

This is a regression between beta1 and the latest updates of 12.04

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: linux-image-3.2.0-18-generic 3.2.0-18.28
ProcVersionSignature: Ubuntu 3.2.0-18.28-generic 3.2.9
Uname: Linux 3.2.0-18-generic x86_64
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.24.
ApportVersion: 1.94-0ubuntu2
Architecture: amd64
ArecordDevices:
 **** List of CAPTURE Hardware Devices ****
 card 0: PCH [HDA Intel PCH], device 0: ALC269VB Analog [ALC269VB Analog]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: alex 1673 F.... pulseaudio
Card0.Amixer.info:
 Card hw:0 'PCH'/'HDA Intel PCH at 0xc0720000 irq 49'
   Mixer name : 'Intel CougarPoint HDMI'
   Components : 'HDA:10ec0269,11790638,00100100 HDA:80862805,11790001,00100000'
   Controls : 24
   Simple ctrls : 11
Date: Wed Mar 7 20:52:04 2012
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Beta amd64 (20120301)
MachineType: TOSHIBA PORTEGE Z830
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.2.0-18-generic root=UUID=3e7b6352-a853-4790-9850-c3388a0291f8 ro quiet splash vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-3.2.0-18-generic N/A
 linux-backports-modules-3.2.0-18-generic N/A
 linux-firmware 1.71
SourcePackage: linux
StagingDrivers: mei
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 02/08/2012
dmi.bios.vendor: TOSHIBA
dmi.bios.version: Version 1.60
dmi.board.asset.tag: 0000000000
dmi.board.name: Portable PC
dmi.board.vendor: TOSHIBA
dmi.board.version: Version A0
dmi.chassis.asset.tag: 0000000000
dmi.chassis.type: 10
dmi.chassis.vendor: TOSHIBA
dmi.chassis.version: Version 1.0
dmi.modalias: dmi:bvnTOSHIBA:bvrVersion1.60:bd02/08/2012:svnTOSHIBA:pnPORTEGEZ830:pvrPT224L-009025:rvnTOSHIBA:rnPortablePC:rvrVersionA0:cvnTOSHIBA:ct10:cvrVersion1.0:
dmi.product.name: PORTEGE Z830
dmi.product.version: PT224L-009025
dmi.sys.vendor: TOSHIBA

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Mathieu Cossette (mcossette)]

!!!When it will work out of the box !!!!

[JaSauders (jasauders)]

Myself and a co-worker just received Toshiba Z385's. We're both on 12.04, completely updated, and we're both experiencing similar issues. Our Fn brightness controls work from a fresh boot. Once the laptop is suspended, then resumed, they no longer work. The brightness meter still goes up/down as if the brightness is changing, but the actual brightness level does not change. It's also worth noting that Fn-based sound controls, wireless toggle, etc. all work fine. It's just brightness it seems.