Let me throw in my two cents worth on this subject. I too have winter cut Osage-orange for fence posts and placed them in the ground and they grow limbs, but not root. They seem to be able to store a lot of growing energy. I thought too they were rooting, but by late summer they die. This is in a low wet area with a high water table and if they will root this would have been in my opinion a good place. The posts were about 8 to 10 inches in dia.
Plant Propagation in Pictures by Montague Free says Osage-orange can be propagated by root cuttings but doesn't list it as propagatable by cuttings taken above ground.