The tech just summed it up as a manufacture fault. He didn't try to explain it. Then again, I'd already told him what it (probably) was, and seemed to agree; or at least not try and correct me. I'd guess that the debris was introduced when the camera module was assembled, but was not in the path of the optics. Jarring or even a temperature change could have caused it to relocate to the sensor; where it seemed determined to spend the rest of it's pesky existence.