Thomas' Christmas Party - S1-E26
Audio problem: (Only in the George Carlin narrated American version) At the end of the episode, when the engines are singing "We wish you a merry Christmas", you can briefly hear Ringo Starr's original narration.
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.
Thomas' Christmas Party - S1-E26
Visible crew/equipment: When Toby puffs by at the beginning, a camera shadow is visible on the bottom right corner.
Answer: Breakdown trains help the engines back on track.