Pullman coaches - weird effect

A steam train hauling Pullmans came through Richmond station on the journey home. Quickly managed to get the phone out, managed to miss the locomotive but got a coach.

I've had this weird effect with the Blackberry before - it's as if it doesn't take the snap all in one go, but the left-hand side seems to be done in sequence, top-to-bottom. Is there a more scientific explanation?