Both shafts should spin always. The vehicle is full time four wheel drive. You can temporarily drive on one driveshaft(either one), but the flange still spins. Both flanges should spin, normally. Something is still amiss on your transfer case.

Edit: one driveshaft requires cdl engaged if you have it.

 

I believe that is wrong thinking for the discovery. If both driveshafts are connected of course they will spin because the axles are moving. If you take one driveshaft out it will not move because its acting like a limited slip diff. One axle is got pressure on it so it moves it to the other driveshaft of least resistance. Mine will not move with the front shaft out. That's will two different Tcases. Mine is a 2002 and I don't have the CDL. If I am wrong please correct me but Im pretty sure this is how the discovery works. I can not move witht he front shaft in and back shaft removed. If I had a CDL I could lock it and make it move but I don't so it shouldn't go anywhere. The truck now runs and drives fine.