Nose up? This happens to me if I get the nose up (well, it's more like tail down, because I'm ripping on a straight line but let the back of the plate drop through the whip) and I'm throwing into a tailwind. Can you see the top of the flight plate? Also, the sabre's aren't the best flex discs; they tend to hold a line pretty well, then stop and drop. You may be getting some off axis rotation and lack of follow through, there are a number of possible causes of your problem. Perhaps an idea of how far and high you're throwing the disc. When you throw the sabre with a hyzer, is the same problem still happening?