Originally Posted by PHMX
I have forgot to mention, but it has most likely to do with weight distribution and center of gravity that'll cause undesired rolling when the speed increases. Not sure if this could also cause a sudden turn though.
I'm no engineer, so maybe we can put our thoughts together and solve it. Maybe the winglets aren't the problem.
As I understand it, lift is dependent on angle of attack. If the wings are aligned in parallel and symmetrical, this produces lift perpendicular to the surface.
If one wing is out of alignment, at a different angle, it will lift more or less, and cause the craft to roll on its axis.
But...there are much more knowledgeable folks here who could debunk that I'm sure.