Strange problem. If "point at camera" is checked, your sunlight will always follow your camera, but if it is unchecked, it stays where it is. I never experienced anything else. Are you sure your box is unchecked and it's really the SUN LIGHT following your camera? Maybe you're using several directional lights, and every one of them has the "point at camera" checker.

Anyways, the easiest way to stop your light from following your camera is to go to Frame #1, delete it (best with writing down its position and rotation) and then make a new one with the same data. Should not take you more than 15 seconds.