Another thing to look at is plant vs. pull timing. Your plant foot should touch before you start to pull or else like someone mentioned above you rotate off line and your plant foot is actually to the right. I was doing this (still do at times) and when I would come through and pull the disc would come out and I would be looking straight down the line, just my line had moved to the right.
Another way to put it (how I saw it first) is located in the technique repair on the main section of the site:
Your timing between the footwork and pull-through are off.
Possible Fix:
Timing is very critical to a powerful and accurate throw. Fractions of a second count and these are probably the toughest issues to spot unles your timing is way off. A fluid, well-balanced x-step is necessary. If you are trying to step too fast or too slow, or your steps are too long or too short, it will be impossible to keep your desired disc orientation, release point/angle, and timing.
Throws that grip-lock are often due to an early pull-through. Starting your shoulder rotation and pull through before your plant foot has landed is almost certain to end up grip locking. The rhythm of the throw should flow 1-2-plant-whip. A 1-2-whip/plant or 1-2-whip-plant is going to cause a very bad griplock/anhyzer problem. If you are finding your throws ending up way right you may want to focus on this. If you find yourself pulling early you may have found your culprit. This problem will take a bit of work to fix but be persistant with it and focus on your timing until it becomes automatic. Be very careful that you do not over compensate. Throws that end noticably left are generally due to a late weight transfer and/or late rotation of the shoulders.