When connecting two USB keyboards to the computer running Linux/xorg, then they both act as single keyboard, which is OK. Pressing keys on one or another keyboard will result exactly the same and both keyboards share the same NumLock state.

The issue: The NumLock LED does change the state only on the keyboard where the NumLock was pressed, but the NumLock state is assigned to all USB keyboards. (Keyboard LED-s are controlled by OS)

Fix proposals:
1) NumLock LED state message is sent to all keyboards when changed.
2) All keyboards have its own NumLock, CapsLock, e.t.c state independent from other keyboards.

Other observations:
1) M$ Windows 7 does send NumLock LED status to all attached USB keyboards.
2) Laptop keyboards have its own driver / hardware numlock handling and therefore these can have independent numlock state. Although on Linux, it can get confusive: I've seen state where USB keyboards NumLock LED has to be OFF for the numpad keys to be handled as numeric keys on laptop.