A lot of carbon arrows have what I'll call a lateral line down the shaft due to the way they are made (wrapped) so they don't have a consistent spine the whole way around the shaft. There is a weak side and a stiff side.

Some guys float their arrows in water and the stiff, heavy side will sink and the lighter side will be on top. Others, like me, shoot a bare shaft and get it as close as we can by tuning the bow. But if some arrows won't tune right then just turn the nock (index) in the shaft 90 degrees and try it again. If this doesn't work then turn the nock another 90 degrees and try again, etc. All you're really accomplishing is trying to get all your arrows to leave the bow the same way. It all depends on anal you are about your equipment.

Then of course, every once in a while you just run into that one shaft that just doesn't act like the others no matter what you do. That's where cut-off saws come in handy. LOL.