Consider this possibility. At very low speeds, such as backing out of a driveway covered with ice, if all wheels lock up simultaneously the computer thinks the vehicle is stopped! I've been able to demonstrarte this many times on a variety of MB's. The two things necessary for this to occur are 1. Vehicle speed is low(<5mph). 2. The road surface is sheer ice! When we have these conditions in my neck of the woods, I make it a point to show my trainees that this is possible.