Two anonymous sources spoke to Reuters about the last-minute production change. Apple had reportedly decided on a single layer of backlight film in an attempt to make the iPhone 6 screen as thin as possible. The company purportedly changed its mind after seeing the screen (it wasn't bright enough) and requested that suppliers redesign the phone to accommodate the standard two layers of backlight film.
It's not clear if the switch could "delay the launch or limit the number of phones initially available to consumers," the sources told Reuters.
There is a glimmer of hope. The sources said that suppliers are working "flat-out to make up for lost time," in order to meet the scheduled Sept. 9 product launch.
It's not uncommon for Apple to make last-minute changes to its products. Shortly before the launch of the original iPhone, production was held up after the company decided to opt for a glass surface rather than a plastic-glass touchscreen.