the 00 E320 did this upon downshifting. when transitioning from dbl to single
digit speeds it would suddenly jerk and (I cant remember exactly) shift into
1st as if synchro wasn't working or some such. after several trips to the
dealer, the Starmark took over and the transmission was replaced.
i've not had this with the 99 E320 but here is a thought: why not wipe out
the adaptive settings? here is a technique which seems to have some folks
enthused about the results, precluding the need to take the car to dealer to
have this performed:
1. Turn the ignition key to the on (not start) position.
2. Press the gas pedal to the floor and hold for five seconds.
3. Turn the key to the "off" position (don't remove the key), then release the gas pedal.
4. Wait at least two minutes for ECU to reset.