Comment 29 for bug 313514

Binary package hint: xserver-xorg-input-evdev

package Version: 1:2.0.99+git20080912-0ubuntu5
Ubuntu 8.10

Keyboards can use keycodes that go above 255. See
These are often multimedia keys for keyboards and remotes.

These are ignored by the evdev driver:
gimble:~/xserver-xorg-input-evdev-2.0.99+git20080912$ grep 255 src/evdev.c
    if (code > 255 && ev->code < KEY_MAX) {
    /* The X server can't handle keycodes > 255 anyway, just drop them. */

Which means they never reach X and therefore cannot be used in anyway.

The only workaround at the minute would be to use input-kdb to remap all keys for an input device to values lower than 255.