With some lifters I've found that the pelvis may swivel posteriorly and it looks like the lifter is humping the air. Rebound is weak and the lumbar spine may be loose.
Also, if the lifter has it in their head to squeeze the hell out of the cheeks, it may keep the hips from rebounding back and the chest from going forward.
Some people have no issue with it. But if I see a problem with the hips not rebounding, it's one of the things I look for. The other things being "tightness" and balance.