transfer case

What is your question?

I was in the process of changing a left front weel bearing. The truck was in park with the e-brake on. I took the front drive shaft out and the truck started to roll backwards. My question is, when the truck is in park shouldn't the transfer case hold the back axle from turning? It holds the front from turning. Is my transfer case screwed up? After i replaced the weel bearing i started the truck and put it into drive with no front drive shaft, nothing happend no forward or reverse? I put the shaft in and everthing worked. Is this denali a front wheel drive truck and rear wheel part time? I know now that my e-brake pads need to be replaced, they don't hold for squat.