From what I can see, it seems the board has some kind of load sensing built into the functions. I have noticed in my earlier testing for my class lights that on initial power up the board illuminates the LEDs dimly for a split second, which suggests it's checking what's there with low current and adjusting itself to supply the correct power for the load.
In my earlier tests I had a red and green LED in parallel with one of the functions, I had a 1K ohm resistor in series too. The function would only allow the red LED to turn on when I activated it, suggesting it lowered the voltage to be around 2 volts. Which is enough for a red LED to light up, but not enough for a green or white LED.
Upon adding a 1N4001 diode in series with the red LED, which has a 1.1 volt drop. It allowed the green and red LED to light up, since the voltage drop across both LEDs was now 3 volts. Which fully suggests my theory that the function grounds are not just direct contacts to ground, but can vary their power as needed.
This wouldn't be anything new, vehicles with canbus on exterior lights also have the capability to check the load. By pulsing a low current through the light circuits, it sees what the load is, figuring out what's burnt out and what's normal. Normally it's for vehicles with incandecent lights, which need a lot of current to make them light up, so you wouldn't normally see the load checking. But add low power LED lights to the circuit, and then you will see the load checking function in action.
But I digress... Not trying to derail my own topic, just mentioning it's not out of the ordinary since it's a system that already exists in other applications
