I had the same problem with some I purchased online. I emailed both the shop where I purchased them and Hoffman Fabrics. I was offered a replacement from both places. Hoffman's replied that there had been some quality control issues at the factory in Indonesia where the strips are cut which have now been taken care of, but that there may still be a few out there that don't meet their standards. Perhaps yours is one of them.
It's disappointing that the shop you purchased from won't replace them. I would definitely contact Hoffman fabrics since they are the fabric manufacturer.