I don't know the circuit or the motor off the top of my head.
My question would be the physical situation concerning the load on the shaft.
*steve*'s Google search answer sounds like the culprit, but as a secondary consideration if that doesn't pan-out:
Just before the motor starts, is there any type of imbalance on the shaft load that would
cause it to turn in the opposite direction for the second or two when the motor is
energizing? The opening of a damper that would create a back-draft that would start
the load on the shaft turning backwards for an initial motor start-up?
A bent pulley, that could allow the weight of the load to start turning backwards at motor
start-up from a neutral position?
The issue sounds electrical, maybe the motor-type has a construction feature that
could allow this to happen if an internal (or external control) component failed.
I'm just offering the physical idea, because it sounds like your cousin might already
be aware of specific electrical issues, and the physical doesn't come to mind.