It's the same symptom of the TJ's design. When lifting it greater than 4" or more, with the front axle hire than the rear axle, the rear axle will crawl underneath the vehicle rather than push it, as the rear axles does this, the front gets lighter. That's one of the biggest reasons the aftermarket went with a long arm suspension lift. Not only does this negate (not to 0, but much lesser) the rear axle walk effect, but the design also negates the effect of the track arm design.