When changing lanes @ app. 45mph, the car initially felt as if it would roll over. the car then swerved right and left , nearly pushing me into the traffic in the next lane. steering was very difficult to control, requiring my full strength. after a few minutes, the car straightened and steering effort returned to normal.this occurred on a smooth, 4-lane road which was dry. jaguar service personnel were aware of similar issues but cold not identify a cause.