non serious answer
its your squat spotters baby!
the iliacus and psoas muscles combine to form the iliopsoas...
as you can see these muscles reside under the lower abdominal wall. Squatting for powerlifting...the wider stance..more bending over (
) ...more use of the glutes cause these muscle to hypertrophy thus pushing the abdominal wall forward.
you have probably permanently changed the way you squat ...and i'm sorry you cant go back to before..
you cant very well make those muscles small now they they have grown.
Since you began powerlifting you use the iliopsoas muscles more to help out your quads..which in turn(your quads) are comparatively weaker now..
however the sum of all parts..ie all muscles working together is greater..ie you lift more weight and now have to deal with a belly thats sticks out!