Nothing I have read suggests that there was any widespread short dropping by BC crews. There may of been incorrect drops over Germany/France/Italy, but drops into the North Sea are almost out of the question.
After-all, a crew is a crew. Its a pretty hard thing to short drop unless the pilot, bomb aimer, navigator ect all agree to do it.
I'm sure it happened, but not often for reasons of cowardice. The bomb was king, and it was these guys jobs to ensure that they delivered it to the target (or what they thought was the target.
Besides, it was probably easier to fake a mechanical error than to short drop once in the air. Radio, nav equipment, bomb site, engines ect could all mysteriously 'fail' and cause an abort.
Most of the Bomber Command pilots were well trained and pretty determined. BC had a surplus of pilots pre-war, in fact it was the ONLY service branch with excess pilots in 1939. Up until 1941 it was operating on the 'flying club' pilots, before newly trained crews began to appear in strenght. Early on gunners and radiomen were quite often ground crew who were just along for the extra pay that it offered.