I seem to recall on my assistant instructors course in '95 that above
maneuvreing speed one should not use any more than 1/3 of full
deflection on any control, and in combination even less than that, since
that would overstress the aircraft. Isn't it likely that in doing what
you did at VNE you were flying the aircraft outside of it's design
limits and therefore ran into an aeroelastic phenomenon which caused the
wing twisting you observed because the wing had been stressed outside
the limits of its torsional stiffness?

Rgds,

Derrick Steed