James and the Trouble with Trees - S5-E5
Revealing mistake: In the end of the episode, you can see James doesn't have his face fitted on correctly, as the gap between it and his eyes appears to be exposed.
Revealing mistake: In a close up of Stepney at the beginning, his lamp iron has a burn mark.
Revealing mistake: When Stepney is returning home through the fog, the source to power his lamp is visible.
Revealing mistake: The rails to the buffers are broken as Toad leaves the siding.
Revealing mistake: When Toad switches lines to avoid Gordon, the track ends in bushes.
Revealing mistake: The old engine's model, who fell off the bridge, was actually Skarloey's, as some red paint can be seen.
Revealing mistake: A wire can be seen between Rusty and his coach after the workmen have removed the ice from Skarloey.
Answer: Breakdown trains help the engines back on track.