Comment 31 for bug 1000146

After digging this issue more, I found that it's not only gnome-settings-daemon's
(nor xfce-power-manager's) problem, but X key mapping's problem.
There is no display toggle key defined in X, so X can receive the key 0x1af
which is defined in kernel
#define KEY_DISPLAYTOGGLE 0x1af /* Turn display (LCD) on and off */

That means all the applications based on X can get that keyevent.
I'm actually a kernel engineer, so I need to find other guys to get involve this issue.
And as far as I can see, this is not the easy one and take time to drive.