Possibly just another example of Manufacturer Supply Line issues, getting common with offshore manufacturers. Chinese suppliers in particular have a tendency to substitute materials or procedures after the firm is vetted and the product is approved.
Of course it might just be a manufacturer's production issue that was not caught in periodic quality control monitoring, but it seems in this case the line itself is substandard and unsuitable for use in the application, rather than a typical manufacturing defect, which points to the first issue rather than the second.