I am not sure of the scientific research, but my son has had a very similar experience. On the other hand, his uncle has mixed dominance and was an amazing student in all areas as well as a skilled athlete (played baseball at the college level).

Does your child cross the mid-line? If not, I know that this is a risk factor that is often used to diagnose SPD and motor issues. You raise a good question - I'd love to know if there is any data supporting what we have seen with our children.