And why not? If the supernatural can manifest messages on walls, it can surely add frames to a film.

Yes. And it's awful, because the physical record of a moment isn't supposed to alter after the fact. It's one thing to see something in a video that isn't there. It's another thing to have it be there—now, as if it always had been—but it wasn't. All ghosts are dislocations of time, but most of them are not retroactive. More hauntings should try it. (More people should not.)