Quote Originally Posted by ccga3359 View Post
What's happening is uneven tension of the threads through the machine. This can also be achieved when sewing by hand (and better controlled). Sailmakers use this to put curvature into the sails.
Another potential issue is the difference in the content of the thread vs. the fabric. If one has more cotton than the other, for example, as it is washed, etc., they will contract differently, causing a roll at the pleats.