Comment 3 for bug 222171

sudo su
echo 10 > /sys/devices/platform/asus-laptop/ls_level

Solves the issue. Issue is related to improperly set ls_level for light sensor on asus laptop.
Light sensor could be disabled by entering
echo 0 > /sys/devices/platform/asus-laptop/ls_switch

Unfortunately this must be done every restart.

I scripted it and added it to modprobe.d default level.

To have the fn+F5 and fn+F4 keys back working simply edit:
sudo gedit /usr/share/hotkey-setup/asus.hk and paste the following:

setkeycodes e005 $KEY_BRIGHTNESSDOWN # Brightness down button
setkeycodes e006 $KEY_BRIGHTNESSUP # Brightness up button
setkeycodes 6f $KEY_MUTE # Mute key
setkeycodes 6d $KEY_VOLUMEUP # Volume up
setkeycodes 6e $KEY_VOLUMEDOWN # Volume down
setkeycodes e007 $KEY_SWITCHVIDEOMODE # Fn+F7 (backlight on/off)
setkeycodes e00b $KEY_VIDEOOUT # Fn+F8 (display switch)