It's normal and acceptable.
Want to get a headache? Think what happens when you make a turn. The front axle makes a much larger arc then the rear, therefor it travels further. To what degree this happens is related to how hard the front wheels are turned.
There are reasons why 4WD should not be operated on hard, high traction surfaces. Low traction, tires are going to slip a little (maybe a lot) so you use 4WD to get extra traction. You are still going to have slip, it is required with a part time 4WD locking the front and rear axles together solidly (without a center differential).