MicroP.dll appears to be linked to this somehow. I stopped that dll and the kb light stopped working until I rebooted.
You can see it in the reg under HKLM\Drivers\BuiltIn\KeyLight
There's also an interesting entry under You can see it in the reg under HKLM\Drivers\BuiltIn\KeyPad called DisableKeyLight
I ran across
THIS THREAD over at XDA where someone was playing with these registry settings.