Mechanical Jack problems of the 1999 Nissan Quest

I placed my van in my garage, which is level and smooth. I raised the van with the screw jack as specified on the screw jack. The screw jack has a lower part which is below the screw, and an upper part which is above the screw. When the tire lifted off the ground, the screw jack immediately bent backwards at approximately 20 degrees. As it was dangerous to life and limb, I immediately lowered the jack. Once lowered, the jack returned to its original shape as if it were made of spring steel. I videoed the jack in the upright and bent position and in the lowered position. The danger is that if the tire needs changing out on the road, where conditions will not be perfect - as in my garage - that jack will bend back and the van will fall and someone will become very hurt.