Ford Explorer ABS problems

I have a 2000 Explorer with 95,000 miles. If I touch the brakes when moving very slowly (parking, final approach to a stop sign)the ABS system kicks in and releases the brakes for a second, allowing the truck to move forward another foot or so. This is very annoying, to say the least. It doesn’t happen when braking at normal/highway speeds, just very low speeds. The ABS light has not come on, and Ford says they can’t do any thing until it does. My mechanic plugged in his diagnostic device and he said when the problem occurs, the device showed both front wheels turning at 158 mph! He doesn’t think it’s the sensors on the wheels. Has any one heard of a problem like this?

My 16 year old son is going to be driving this car and I really would like to get it fixed. Any one have any suggestions?