Jim, did the down bag have moisture in it, or just on the surface? Was it on the surface close to the sleeper or the outside surface exposed to the air?
Edit, it looks like you are saying on the top surface exposed to air, just making sure I am reading it right.
Edit Edit. Could the moisture have come from the fact that the upper side of the down bag was cold/not warm, so moisture would condense on the outside just like it would on the inside of the tent, rather than moisture coming through the inside?