Heck of a jump.
More likely is that your back is rounding too much, causing some compression where it shouldn't be in the spine and making the fibers fire all wacky in your back.
Major points of flexibility in the full squat:
Calves - both gastroc and soleus
Hamstrings - you should be able to touch the finger tips of both hands together around your foot doing a modified hurdler stretch with little to no back rounding. (not exactly the same for everyone, that's just a point of reference to start with)
Hip area - all the glutes, piriformis, adductors, abductors
Hip flexors are a big one
Chest/shoulders - tightness here can cause you to have to round a little in the upper part of your erectors and lose balance a little
I personally have to stretch for about an hour to get loose enough for a full squat workout, but I spend all day sitting in class and at a computer. You may need less.