If I had to guess, I would say that they are warped. The elevator halves on my Fliton Extra were warped (still are a little bit I think). So were the ailerons and the rudder. MinnFlyer gave me a tip: bend the surface in the opposite direction of the warp/twist, hit it with a heat gun, and see if that straightens it. You may have to go back and forth, and do this several times, but it will straighten out.