i tend to bend too far forward while doing squats. i am very flexable but for some reason when i do back squats i just never feel right UNTIL i started squating with my heals on a 2x4. the very first time i tried using a 2x4 i got one of the best leg workouts ever. this might not be the best idea for powerlifting but it made a world of difference for me.
this is an issue with hamstring flexibility
start stretching them daily