Comment 1 for bug 543294

In case that the original submission is unclear, here's my situation in UL30A-A2.

Expected behaviour:
fn+f5 lowers brightness, fn+f6 increases brightness. (worked well in Karmic)

Observed behaviour, in Lucid Beta 1:
Initially, when the computer is first booted, it responds to f5/f6 but in random behaviour.
For example, if I press fn+f5, it would lower the brightness, then increase it to the maximum, repeat a couple times, and back to somewhat random value somewhere in between.
After the initial reaction, fn+f5/f6 key no longer causes any change in brightness - for a couple minutes. For this period, acpi_listen does not seem to print out anything when these keys are pressed.
After a couple minutes, these button presses seem to "queue up" and cause random changes to the brightness again - acpi_listen reports these values.

video LCDD 00000087 00000000
hotkey ATKD 00000025 00000017
video LCDD 00000087 00000000
hotkey ATKD 00000025 00000018
video LCDD 00000086 00000000
hotkey ATKD 0000001b 00000005
hotkey ATKD 0000001b 00000006
video LCDD 00000086 00000000
hotkey ATKD 00000021 00000001
video LCDD 00000087 00000000
hotkey ATKD 0000002b 00000008
hotkey ATKD 0000002b 00000009
video LCDD 00000086 00000000
hotkey ATKD 00000021 00000002
video LCDD 00000087 00000000
hotkey ATKD 0000002b 0000000a
hotkey ATKD 0000002b 0000000b
video LCDD 00000086 00000000
hotkey ATKD 00000021 00000003

Changing the brightness manually with xbacklight shows similar behaviour - random changes, or periods of no change.
Using Gnome-power-manager's brightness control slider behaves the same way.