Comment # 13 on bug 1040718 from Stefan Dirsch

> [...]
> So they are both doing what they are supposed to do, but changes in one are not > reflected in the other (which may be exactly how it is supposed to work)
> [...] If this is working as it should, then this bug can be closed. 

Honestly, I don't know. :-( Daniel may know though for NVIDIA's driver.

I guess most people are just happy with backlight control keys working on their
laptop, which is probably using /sys/class/backlight/acpi_video0/brightness.