Comment 29 for bug 6628

> sudo /lib/udev/keymap -i input/event6 doesn't output anything

Hm, that is weird, and will most probably be a kernel bug. However, just to be sure that we tested everything, could you please run it against input/event4 (the main keyboard) as well? If that doesn't react to Fn keypresses either, then as a last resort you might try all input devices from input/event0 up to the point where it says "no such device".