Help w/twisting double yarn prob

[fitcook]

I am pulling two strands of the same wool (from two different balls) and knitting a purse in the round. The hanks were wound into center pull balls at the LYS. I am pulling the yarn from the center of each ball but the strands are getting horribly twisted after a dozen or so stitches; I even tried pulling from the outside of each ball and the result was the same: I have to keep stopping and dividing the yarns, untwisting the strands, and otherwise NOT knitting or I will just have a bunch of KNOTS. The balls are sitting side-by-side in a small bag so they are not rolling around or otherwise spinning. Any tips, PLEASE?!

[Hildegard_von_Knittin]

I don't know if this will help, since you've already started, but when I use a double strand of the same yarn, I pull from the center and the outside of the same ball. If you're using wool, you could just break one strand of yarn, find the outside end of the yarn you didn't break, and attach it using spit-splice method.
Or maybe you could put both balls IN the bag you're knitting.... then there wouldn't be any long strands hanging down that would twist. :??