Comment 154 for bug 207473

The same problem. 4 events. The brightnes in/decrased by 2 steps:
Ubuntu 11.10 Unity
Ubuntu 11.10 Gnome-shell

$ cat /sys/class/dmi/id/sys_vendor
Hewlett-Packard
$ cat /sys/class/dmi/id/product_name
HP Pavilion dm4 Notebook PC

$ sudo killall gnome-settings-daemon
$ /etc/init.d/acpid stop
$ /etc/init.d/hal stop (No such file or directory)

$ sudo /lib/udev/keymap -i input/eventX
.....
# single decrease brightness button pressed
got scan code event 0xAB without a key code event
got scan code event 0xAB without a key code event
.....
# single increase brightness button pressed (YES !!! the same key-code)
got scan code event 0xAB without a key code event
got scan code event 0xAB without a key code event
.....

$ xev | sed -n 's/^.*state \([0-9].*\), keycode *\([0-9]\+\) *\(.*\), .*$/keycode \2 = \3, state = \1/p'
...
# single decrease brightness button pressed
keycode 232 = (keysym 0x1008ff03, XF86MonBrightnessDown), state = 0x0
keycode 232 = (keysym 0x1008ff03, XF86MonBrightnessDown), state = 0x0
keycode 232 = (keysym 0x1008ff03, XF86MonBrightnessDown), state = 0x0
keycode 232 = (keysym 0x1008ff03, XF86MonBrightnessDown), state = 0x0
# single increase brightness button pressed
keycode 233 = (keysym 0x1008ff02, XF86MonBrightnessUp), state = 0x0
keycode 233 = (keysym 0x1008ff02, XF86MonBrightnessUp), state = 0x0
keycode 233 = (keysym 0x1008ff02, XF86MonBrightnessUp), state = 0x0
keycode 233 = (keysym 0x1008ff02, XF86MonBrightnessUp), state = 0x0

I think that's all...

Binding these commands to other hotkeys helps me.... not critical but ....
xbacklight -inc 10
xbacklight -dec 10