Actually, it did it "all the time". I found out about this while being stuck in traffic, and seeing the lights move slightly up and down while inching forward and stopping. It was visible because it moved in discrete steps, compared to the continuous movement of the car.
I hadn't known it was a thing before, and went looking in the owner's manual for confirmation.
I hadn't known it was a thing before, and went looking in the owner's manual for confirmation.