I was sharing with James an article discussing bend-twist in beams. It describes how the different forces acting on and within a beam will cause twist. Basically if a beam (bow limb) is asymmetrical in strength, it will bend towards the weak side. They also discuss how direction of fibers can cause twist as well, similar to what we see in boards due to asymmetrical strength in different directions. The corrections would be to make the strong side weaker, or bring the string nock on the weak side inward.