I would imagine that the Sprinter may have an OM606 rather than the OM603.

On the OM603, the front hub has a woodruff key clocking it to the crank. The clearance is very tight, between, the hub slot, key and crank cutout. It is possible that the key may have sheared, or is missing if the hub was pulled off and then reinstalled knocking the key into the oil pan. It's very finicky due to the tight tolerances to get the three aligned perfectly when installing. For the hub to rotate off of the crank stub in either direction, the key must be sheared or missing. The bolt and washed serve only to lock the hub onto the key and should not be affected by rotational forces.

I can't confirm if the OM606 is configured the same way, but likely, it is/has been a common practice on many engines for a long time.

Best of luck