So this value is a pain since 3.0 came out. When you travel that value it's at that moment the auto footstep turn on and off. Making the entire character snap. Not sure what is happening to the IK at that moment as well, but the hip act differently.
Disabling auto footstep in the avatar descriptor will Fix the snap when jumping (gif 2) or passing 0.65, but the hip drifting will remain above it that value(gif 1). But no more auto footstep make the character glide around the floor.
Here an avatar you can toggle pose and see the difference between above and below 0.65 upright.
avtr_dca7043d-adc2-4ebb-bfa7-bbb3ddcfdd17
The behavior wanted when using any of the pose is when upright is below 0.65.
For when you are jumping or crouching, the auto footstep behavior off is the wanted.