Revealing mistake: At the beginning of the episode, the end of the set is visibly reflected of Gordon's smoke box in a close-up of Gordon.
Edward, Gordon and Henry - S1-E4
Revealing mistake: When Gordon passes a signal, the track under him wobbles.
Revealing mistake: When Gordon puffs into the ditch his face looks wonky and wires are visibly attached to his cab.
Thomas and the Breakdown Train - S1-E7
Revealing mistake: The breakdown train appears to be missing in the close-up shot of James' wheels being put back on the rails.
Thomas' Christmas Party - S1-E26
Revealing mistake: In the very last shot of the episode, loads of wires are visible in front of the engines and behind the turntable.
Revealing mistake: When Henry passes under the bridge, a tree shakes, giving the illusion that the stones were thrown. When in reality, Henry actually ran right through a low-hanging branch.
Revealing mistake: When Gordon falls into the ditch, wires under his cab are visible.
Thomas and the Breakdown Train - S1-E7
Revealing mistake: Thomas is taking on water in the opening shot, but his water cap is closed.
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.