Wrong Road - S2-E22
Revealing mistake: When Gordon says, "I am Gordon! Stop! Stop!", his eyes are wonky.
Visible crew/equipment: When Diesel is on the turntable, camera equipment is reflected in the windows for several moments. (00:02:00 - 00:10:00)
Visible crew/equipment: When Bill and Ben are shunting, we can see hands. (00:02:00 - 00:10:00)
Revealing mistake: Most of the engines' eyes are wonky when Diesel says their names and their eyes are wonky in a few shots of them.
Wrong Road - S2-E22
Revealing mistake: When Edward crosses the viaduct, the last coach of his train does not have lighting.
Character mistake: The driver said that Bill and Ben's names and numbers would be taken away, but the twins do not have numbers.
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.
Visible crew/equipment: In the restored version, when Bill and Ben leave Brendam Docks, the twins do not disappear. They just stop right at the top of the screen. The end of the set can be seen in a still from the episode: also, two hands can be seen pulling them backwards with string.
Continuity mistake: When Edward stops at the station, a close up of his whistle shows the sky is sunset dark, but when he arrives, it's bright daylight.
Visible crew/equipment: When Edward sees Trevor for the first time, the edge of the set is reflected on Edward's boiler.
The Runaway - S2-E10
Audio problem: When Thomas is tired and approaching the station, he is moving pretty slow, but the sound of Thomas' wheels moving is like he's going pretty fast.
The Runaway - S2-E10
Visible crew/equipment: When Harold is flying, in one shot, a stage light is reflected off his blades.
The Runaway - S2-E10
Revealing mistake: When Thomas' fireman is ill, you can see a brief flash of red outside, meaning it's James. (Note: same footage from Old Iron).
The Runaway - S2-E10
Visible crew/equipment: When Thomas leaves the station, a tripod is reflected off him.
The Runaway - S2-E10
Revealing mistake: When Duck comes to Terence's field, the end of the track leads right into the bushes right behind duck.
The Runaway - S2-E10
Revealing mistake: When Duck is happy at the beginning, the breakdown train's buffer on the right is broken.
Visible crew/equipment: When Bill and Ben leave Boco and Edward, a tripod is visible in the top right (visible in HD full screen version).
Visible crew/equipment: When Bill and Ben pass a station, you can see a bit of studio equipment at the top of the screen. (Visible in HD full screen version).
Continuity mistake: When Bill and Ben notice their trucks are gone, there are guards in front of them, two shots later, there is no sign of the guards.
Visible crew/equipment: When Duck is being pulled out by Thomas, from the shot inside the barber shop, a camera and other studio equipment is visible behind Duck.
Answer: Breakdown trains help the engines back on track.