Sounds odd to me. Never heard of this.
While on the ground, craw under with a flashlight and poke around. Check that the springs are seated correctly and not accidently seated screwy on a perch. Also check that the sway bar endlinks are not binding and are free to pivot correctly.
Also, while under there, have a buddy push up and down on the rear of the car as you observe what is going on from under the car.