Revealing mistake: In a shot of Gordon arriving at Brendam Docks, only half of his tender is visible.
Continuity mistake: Henry pushes Percy onto the coal tipper twice.
Plot hole: Percy was blamed for being on the coal tipper when it was Arry, Bert, and Henry's fault. None of the three got consequences. Also, why would the workmen tether Percy or even activate the coal tipper when they knew he was an engine?
Audio problem: When Oliver arrives at the station, he has Percy's whistle sound.
Continuity mistake: When Thomas hides behind the trucks, there are only 3. But in the next shot, there is a flatbed with a crate on it in front of the trucks.
Audio problem: At the beginning of the episode, Salty has Diesel's horn sound.
Revealing mistake: When the passengers lift Duncan back onto the rails, his trailing wheels are still derailed.
Audio problem: Thomas has James' whistle sound when he passes Sir Handel at the beginning.
Continuity mistake: When Thomas passes Gordon, Butch's magnet is attached to Thomas. In the next shot of Thomas, it isn't. And in the shot after that, the magnet is attached again.
Audio problem: When Thomas and Butch deliver Rosie's wheel, her whistle sound is at a higher pitch.
Flour Power - S9-E26
Factual error: The narrator says "Suddenly, Thomas felt something touch his tender," but Thomas is a tank engine. "Bunker" is the correct term.
Continuity mistake: When Thomas goes back to Maithwaite, Flynn's railway wheels are not touching the rails, but his tires are.
Continuity mistake: After Thomas stops near the bridge, he does not have a Wonky Whistle.
Audio problem: Stepney's whistle sound changes throughout the entire episode. And in the UK and other versions (excluding US), Gordon, Duck, and Douglas have the same whistle sound.
Bowled Out - S4-E18
Audio problem: When James leaves Crovan's Gate, he has Smudger's whistle sound.
Audio problem: When Den and Dart bully Flynn, their voices are swapped.
Continuity mistake: When Flynn sprays Edward, the water goes over Edward, but somehow his driver gets wet. And when Flynn sprays Gordon, the water is seen hitting the platform and Gordon's tender. Later, the water is seen hitting one of the coaches.
Factual error: In the U.K. narration, when Flynn sees Gordon, the narrator says "Flynn steamed in to a stop." but Flynn isn't steam powered. This mistake is fixed in the U.S. narration.
Dirty Work - S2-E13
Visible crew/equipment: When Duck bumps a truck when the Troublesome Trucks are singing, "Pop Goes the Diesel", you can see a string pulling the truck.
Answer: Breakdown trains help the engines back on track.