When you're in part-time 4WD on a hard, dry surface, the vehicle is going to buck when turning as the front wheels are fighting the back wheels as they both want to rotate at different speeds. All part-time 4WD vehicles will do this.
And this is hard on the drive train. That's why they call it "part-time." You don't want to leave it in this mode for regular driving.
The AUTO mode solves this problem by running in 2WD and only engaging 4WD when a loss of traction is detected.