To throw the ball cross lane you naturally get your hand to the side more. Just watch anybody, it doesn't have to be a forced thing, its just that (for most ppl) the arm is goin across the body to some degree atleast and this gets you more on the side of the ball. I used to be all screwed up, I could throw my spares, didn't matter where with perfect form, but there was something about throwing strikes that I was spinning the ball some.  I was getting perfect tracking going right, and somehow i was compensating when I went left too, just couldn't go strait. My feeling is that you have a different release for spares. Now what I found was that I was to concerned with hitting my mark and TRYING to get as many revs as possible on the ball.  What I learned to do is simple: RELAX your hand as completely as possible. To remember this, just before you start your approach simply stretch your hand while in the ball. Take that pressure off of the thumb and fingers. Then fire away.  I have probably doubled my rotation if not more since i learned to relax and not try for rotation. It seems odd to let off pressure to get rotation but it works. Now everything I just said may not be anywhere near right for you, but give it a try and see if you don't get a better track.  It sounds to me that you have a tight grip on the fingers and are producing an end over end roll by holding them too long.  Thats just my thoughts and I have never seen you in action so I can't say for sure, but its my best guess. Good luck.