Rotating shape tweens

I’ve drawn a 3-dimensional box using stretched planes and I’m trying to use shape tweens to stretch the box in time (stretching the planes individually). My ploblem is when I try to stretch one trapezoidal plane into another trapezoidal plane, it wants to rotate it as it morphs instead of simply shifting the two beziers I moved. Is there a way I can stop it from rotating? Or is there an easier way to go about this?

I was drawing two boxes as described above and some planes morphed perfectly, some rotated as they morphed, and some wouldn’t let me add the shape tween at all. Any idea why that would be?

Any help would be appreciated.