Illegal wind-up?

Recently in a league governed by NFHS rules an umpire told a pitcher his wind-up was illegal because when pitching from the wind-up he paused his leg at the top of his wind up(while right foot was on rubber and left leg lifted), he told the pitcher that it has to be a fluid motion no pause. I can not find this rule anywhere and I have seen a pitcher from Arizona Diamondbacks(Haren) do it. Anyone ever heard of this?