I have to say that I have made a couple longbows from reflexed staves that I ended up getting the alignment a bit off on too. One fix is to try to steam bend one or both of the limbs in a couple strategic places to try to get it right. If you make the belly too deep on a longbow it can also make it more likely to twist, but alignment is the main thing that will make the decision if it twists or not. One thing that makes me rough out misaligned bows is marking a center line or lay out at all on the bows back to follow. If I just mark the nocks and the center of the handle on the staves back, and then rough it out by eye the rest of the way by looking down the stave longwise while roughing it out now and then, it's much easier for me to get it aligned and straight, exc exc...