There are many reports of both sides 'ditching' their bombs. Only last month I read a first hand report of an 'attack' on a Fleet Air Arm base in Scotland where the the bomber ditched the bombs in the sea. Since it was a clear night and the observers could see the aircraft and the target was very close to the coast - the crew decided not to attack, for whatever reason.
Later in the war, the RAF crews had to take a photograph to show that they were over the target in order to qualify for the trip against their Tour. Whilst many failed to find the target, for many understandabale reasons, some crews deliberately chose not to bomb the target.