I just noticed this is happening to me last night, in a P-38J. Level the plane with auto level, full throttle both engines, and when I turn off auto pilot, he plane begins a slow roll to the left. With the manual control of the P-38s engines, I can control the roll by reducing right engine throttle, but I have to reduce by almost 50%.
I haven't bothered to reset my trim controls, but I have assigned them now to the joystick hat switch and will try manually correcting.