Quote from P76: when you are reversing down a hill under engine braking. The traction control, for some reason, wants to lock up the front wheels. With a CDL, this also results in braking to the rear. Without a CDL, it means that the front wheels lock up and lose traction while the backs remain turning and have traction. This can cause the front to want to pass the back and cause the car to spin sideways on the hill.
I've personally never experienced this situation, but it certainly sounds possible. Something to keep in mind when backing down a hill, especially so if you do not have a locked CDL.