Comment 3 for bug 114953

Here's the keyboard portion of my Xorg.conf:
Section "InputDevice"
    Identifier "Keyboard1"
    Driver "kbd"
    Option "AutoRepeat" "250 50"
    Option "XkbModel" "pc104"
    Option "XkbLayout" "us"
    Option "XkbOptions" "compose:menu,lv3:ralt_switch"
    Option "XkbRules" "xorg"
EndSection

There's nothing there to limit input to a specific device. I'm not the only person to have this problem either.
http://blog.eikke.com/index.php/ikke/2007/04/28/how_to_fix_your_acpi_buttons_the_hackish

However, I'm now running 2.6.22, and 'kbd' and 'event0' handle the power button now so the original version works as expected again.

# cat /proc/bus/input/devices
I: Bus=0019 Vendor=0000 Product=0002 Version=0000
N: Name="Power Button (FF)"
P: Phys=button_power/button/input0
S: Sysfs=/class/input/input0
U: Uniq=
H: Handlers=kbd event0
B: EV=3
B: KEY=100000 0 0 0

All in all, it appears to have been a kernel issue.