Revealing mistake: In the scenes directly before and after Duck's photo is shown, bits of trees by the lineside can be seen floating in mid-air.
Revealing mistake: When the elephant is ushered into the truck, the tracks suddenly stop and look as if they lead straight into the mountain in the background.
Santa's Little Engine - S17-E18
Revealing mistake: At one point, the shading effect on Thomas' whistle is not rendered properly, so it appears silver instead of gold.
Revealing mistake: Each time when Thomas takes a shortcut, the points do not change.
Revealing mistake: When the camera follows Salty right after he coughs, him and his trucks are overlaid on top of the barrels in the foreground for several frames.
Answer: Butch the breakdown truck must have pulled Gordon's tender all the way up the rails so the breakdown train can reach it and also Butch helped to get Gordon close to the winch.