Looks like your problem is with the GCP. To quote their manual (p.12):
NORMAL. The CC message is only sent when you press the instant access button. You press
it once to turn it on, then again to turn it off.
MOMENTARY. This option means that it sends an “on” message when the instant access
button is pressed, then sends an “off ” message when it is released.
Sounds like you have "NORMAL" when you want "MOMENTARY."
