there is confusion in my mind.
are we speaking of the flashing strobe lights being ON while on the ground
or are we speaking of the red rotaing beacon?
most every airline I've worked for (3 small, one huge) uses this protocol:
when electric power is on the plane, the nav or position lights are on (we never turn them off without unusual circumstance)
when engine start is imminent, rotating beacon on.
now, certainly the pilots could have forgotten to turn off the beacon on return to the gate.