Cyanogen mod 7.2.0 keyboard backlight not working properly
After quite some time a friend of mine goofed around and actually found the fix:
CyanogenMod Settings > Display > Automatic Blacklight
In here enable 'Use custom' and then look at the values in 'Edit other levels...'. The levels you want to edit are either the ones under 'Buttons' which are the values for the backlight of the soft keys (Home, menu, back and search) and the values under 'Keyboard' is for the  keyboard backlight. A value of 30 is standard for the 'Buttons' and the values for the 'Keyboard' are only 0 or higher than 0. (Even though you can choose values between 0 and 255, it doesn't seem to matter visibly.)