When reading the described problem, I thought... yep, I experienced that once. It was caused by a CG much too far forward. I'd balanced the plane (Spacewalker II) inverted on a CG machine, to discover doing so did not produce the same results as doing it upright at the wing tips as the directions outlined. After the maiden, I said the exact same thing to the guys... ya can't keep the wings level, it wants to roll off one way or the other. Correcting the CG solved the problem.