You'll find that "Numlock" actually sends "Pause" instead.
I checked some older versions; In v1.5.7 and v1.5.8, this still worked correctly("Pause" was "Pause", "Z" was "Z"). From v1.5.12(the closest version to v1.5.8 still available) onward, it does not("Pause" is "Numlock" and "Z" is "W").