Apparently Ford's system is a bit too quick to see the "problem"
The light is likely being triggered by the ABS sensor input from the rear diff, while the front sensors are simultaneously providing little or no input. The system sees this as a fault and triggers the light (probably also disabling the ABS system until the ignition is cycled).
Probably nothing you can do about it except just not spin the tires (although that might not be much fun if it was while mudwhomping or having fun you were spinning them lol ).
If the light comes on while driving normally though, then I'd say chances are better the fault is real (try pulling the codes. If it says "sensor output out of sync" or something along that line, then its what I mentioned above)
