I had that happen recently when I purchased fabric from one of my favorite, high end lqs. They said it was because it was a batik, but no way. Since the fabric was going to be cut and because I had been looking for this color for months, I took it. They wouldn't give me anything off on it and snapped that they didn't buy seconds. Maybe not, but the threads they're using must be. It must be oil or something getting on the thread and when it's woven it comes into the fabric. We just have to be really careful when we purchase fabric.