Audio problem: Gordon had Duck's whistle sound and James had a different whistle sound in almost every Season 4 episode they appeared in.
A Bad Day for Sir Handel - S4-E6
Revealing mistake: When Sir Handel derails, you can see a small rod sticking up out of the ground from the tracks.
Peter Sam and the Refreshment Lady - S4-E7
Other mistake: In two shots shown at the beginning, Henry is wearing Gordon's upset face mask.
Audio problem: In the US version (Rusty Helps Peter Sam), Peter Sam has a different whistle sound after the trucks hit him. And throughout the episode, a lot of music and sound effects are missing.
Revealing mistake: When the passengers lift Duncan back onto the rails, his trailing wheels are still derailed.
Visible crew/equipment: As Peter Sam passes Skarloey and Rheneas, a camera shadow is seen.
Character mistake: On his way back to the sheds, Sir Handel goes through a red signal.
Audio problem: Thomas has James' whistle sound when he passes Sir Handel at the beginning.
Continuity mistake: When Rusty arrives on the Other Railway, chains are seen hanging beside the signal box, but in the next shot when Rusty asks, "Ooh! What's that?", the chains have disappeared.
Revealing mistake: Dried-up glue is visible around Rusty's face during the line, "Right, we'll find one tomorrow."
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.
Continuity mistake: After Stepney's driver tells Stepney to speed up, Caroline is nowhere to be seen.
Bowled Out - S4-E18
Continuity mistake: When the diesel grinds to a halt and the camera switches to Duck and Stepney and then back to him, he is noticeably further away from the coaches.
Bowled Out - S4-E18
Audio problem: When James leaves Crovan's Gate, he has Smudger's whistle sound.
Revealing mistake: In a shot of 2 vans singing "Pop Goes Old Ollie" you can see a spider crawling on the right side of the left van in the screen.
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.