99' Silverado Front Drive Shaft

I am wondering what the status of the front driveshaft should be when the vehicle is running? I have push button 4x4 and when the truck is running in PARK and in 2wd the front driveshaft is locked.(won't turn freely by hand) I have had other 4x4s that the driveshaft spun freely when in 2wd. They were manual shift though. Whats up on this?