I have only hand quilted one quilt using the Hobb Heirloom 80/20 mix and did not encounter this problem. The batting could be defective or it is possible the backing being a sheet. I have heard that the high thread count on some sheets can make for difficult quilting. It is possible small sections of the sheet are more tightly woven and because it was older maybe those cotton threads drew up tighter in normal shrinkage in small areas of the weave of the sheet. Very unusual problem. I am glad that it only affected small portions of the quilt. I hope you will post a picture of the quilt.