Revealing mistake: When Stepney is returning home through the fog, the source to power his lamp is visible.
Revealing mistake: The end of the set is visible in one shot at the quarry.
Revealing mistake: Duck's footplate clips through the platform at Knapford at the beginning.
Revealing mistake: Before James collides with the tar tankers, he is already covered in tar before he actually hits them.
Fergus Breaks the Rules - S7-E18
Revealing mistake: A wire is under Fergus when he arrives at the smelter's.
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: Breakdown trains help the engines back on track.