Hi,
Sorry about my bad english... its hard to understand!
But Spitfire dont have aileron trim, only rudder and elevator...
Im not expert, but I think if it was a "pre trim" it could be verified on land.
This "bug" is not velocity dependent, it occurs when u leave ground.
If we set all trims to neutral, engine off and prop pitch 0 the aircraft rolls to right. When I compensate the aileron with joystick, forcing to a "neutral" position, the plane flight straight how desirable.