a bushel is a unit of volume.  According to my sources, a bushel = 1.244 cu ft.

a bushel of ear corn should... should .. have the same volume as a bushel of shelled corn.

a bushel of ear corn will not weigh the same as a bushel of shelled corn; however, a bushel should equal a bushel.

1 bushel of ear corn when shelled out will yield less than 1 bushel of shelled corn.  the difference should be the cob.

I wonder if this is really what is happening:

70.7 lb of ear corn (or 72 lb, whichever you think is accurate) is not really 1 bushel; in volume, it is actually more than 1 bushel.  It is the amount of weight that is needed to shell out 56 lbs of shelled corn - or 1 bushel.

Does that make sense?