[xlr8tr]

sounds like mine. I have a triangulated 4 link but the same issue. If you jack up one rear corner i think it demonstrates what is happening: as you jack the one side, the wheel on that side actually moves forward, effectively steering the rear.

I think under acceleration the passenger side compresses, pulling passenger wheel forward steering you to the right. Assuming your links are level at rest. My links are higher at the front (I think that give sit more anti-squat), so I steer to the left under acceleration.

I'm going to put sway bars on, I don't have any, so that should reduce (mask) the problem.