EE was leaning into a 52"" tall box, to remove a remaining scrap of material. the sideflap was standing straight up and there were 2 boxes directly in front of the box. The forklift driver put the forks into the skid and upon lifting it, shifted the box next to it, shifting the box. Because of the flap, the driver did not see EE in the box. He jumped and fell against railing.