Oops, typo in the docs, it should be
keyboard_key_rctrl
, not
keyboard_key_kp_rctrl
.
In addition, the right ctrl is a bit special, since it is assigned to joystick emulation when applicable. This will override the input mapping. So you also need to make sure to use a real joystick - or no host device in the joystick ports (well, anything but keyboard joystick emulation).