for some reason i had the same problem for a little while last year, hadn't had it before, havent had it since! i coated the last 18" or so of the braid with bondage - though superglue would work just as well. it doesnt make it rigid, it just amde it less likely to twist.
the other thing to do is to feather it just before it hits the water - often if you look carefully the lead is a few feet in front of the float due to drag on the float through the air - its that line that twists. feathering it usually untwists it.