It's probably twisting because of the way it's being pulled off the ball. If you pierce the ball through a central post, and pull it out from the side, so that the ball itself turns, then the ribbon won't get twisted. A nice portable tool for this is the "Knitty Walker," which is a bracelet that suspends the ball from the wrist (I'm using one on the front page of this site, although it's hard to see it). The ball holder pivots and turns, free from the bracelet, so it works great. I have a close up picture of it on this thread: What are your favorite knitting accessories?