Irish: "one symptom described was failure of the bolt to stay back after the last shot. shortcycle?"
I know what you mean Irish (& I know it sounds like the carrier is hanging up), but I doubt it. There's really not that much it can be, but if the problem is real -- the buffer is rubbing the tube near the back end. The buffer tube could be OC, or it could be dented -- either one would explain the hang-up, AND what [u]seems[/u] like short stroking at first.
mtnpatriot, take that buffer out, & peek in there -- see any rub marks on one side? If not, do you know how to remove the stock to examine the outside of the tube?
If this is a new gun, clean out the tube (it's probably dry though), & slop a little CLP in there, from your describtion it sounds like it'll wear in just fine.