Sounds like a aileron control reversal issue. It's both an aerodynamic and structural issue just like flutter. Although, unlike flutter it doesn't excite a natural frequency but rather a divergence of the structure. A term for it is aeroelastic divergence. The torsional load produced by the deflected aileron twists the wing which changes the angle of attack of the wing enough to reverse the rolling direction.

This is not my area of expertise, but I have been educated on it. The fix is usually to increase torsional stiffness or limit control effectiveness or lower the redline speed. The divergence speed can be different than the flutter speed. Wish I could comment about the leading edge lead... I can't think of an explanation for now.

On Saturday, June 27, 2015 at 10:07:58 AM UTC-4, JJ Sinclair wrote:
Time for another JJ story. We were finishing at Ephrata at 50 feet and 140 knots in our ASH-25 (with 2 meter wing extensions). As I crossed the finish line, I pulled up and rolled left,. At about 45 degree left bank, I applied right stick to stop the left roll............IT KEPT ROLLING LEFT................I then applied full right stick and rudder and the left roll stopped, but by then we were in a 75 degree left turn. The nose was up, so as airspeed slowed, the ship slowly responder to right stick commands.
After landing, I talked to the guy running the finish gate who was looking right down our wing as we flew through the gate...........He said it was the scariest thing he had ever seen! The wing tip leading edge, twisted down and doug-in, resulting in the un-commanded left turn, the rest of the wing looked like a sign wave. The wing extension had been somewhat blessed by Schleicher who had us install some 12# of lead in the outboard leading edge.. I believe it was to prevent flutter, but probably aided the twist problem.. Any aerodynamic experts explain why the lead was placed in the leading edge? Didn't it help twist the wing leading edge down?

Not too long after that, I sold the ship and retired to the peace and tranquility of the finish cylinder in sports class.
JJ