Perhaps I misinterpreted, but I think DenisM was talking about something completely different. He mentioned that because of a lack of density in the leading photons, the first piece of equipment missed the measurements while the second one picked it up.
That would a problem with the system they're measuring with, not at all to do with treating light as a single entity.
As I interpreted it, the critical part of his explanation is the fact that the higher density part shifted from the back to the front. If that change in density would be due to actual photons shifting that way, then those photons would have traveled faster than light (whereas the entire 'blob', on average, traveled exactly at the speed of light).
Could be explained if the photos leaving the source look like this: :::::..... and arrive like this: :::::.::, where the 'tip' folds back on itself to become visible, still before the original bulk of the photon cluster.
