This has happen with poly.too and usually after I have handle it. Then I have had fabric for 20yrs. and nothing. You have to be careful when you put it away. You may not see anything on your hands or the fabric but go back 6 months there it is a spot and it went through several layers. If you are not sure wrap each layer with tissue paper. I suggest that for fabric that cost a lot. You can store in clean pillow cases. I'm going to look online some more about how to prevent or get rid of them.