Plot hole: James appears in every episode before his introduction in "Thomas and the Breakdown Train." Also, James is supposed to be black, because at the end of the episode, James is told he will get a different coat of paint. (He is also black in the book).
Continuity mistake: The engine sheds change design throughout season 1.
Visible crew/equipment: In the shot of Thomas rolling backwards onto the turntable, look left very carefully, and you'll see a camera tripod visible. Fullscreen version only.
Visible crew/equipment: When Gordon, Thomas and the express round the bend, a camera tripod is visible on the left side of the screen.
Continuity mistake: In a close up of Thomas when Gordon is pulling him, Thomas is not coupled up to Gordon's train.
Continuity mistake: When Gordon approaches the station, in the two previous shots, the background changes from a close up of Gordon to a wide shot of Thomas and Gordon.
Continuity mistake: When Gordon says "Yes, I will" the background disappears between shots.
Continuity mistake: In the shot of Thomas stopping inside Knapford with his coaches, Henry is in his new shape.
Visible crew/equipment: When Thomas is on the turntable, a camera shadow is visible on the left.
Plot hole: How could Gordon's driver tell the station master that Gordon couldn't get up the hill? There are no phones on Gordon's hill.
Audio problem: When Gordon backing down to the bottom of the hill, you can hear brakes screeching, but Gordon's wheels are still moving.
Visible crew/equipment: At the beginning, a camera is visible in the top right corner.
Other mistake: Edward is wearing James' sad face mask when he approaches the water column.
The Sad Story of Henry - S1-E3
Audio problem: When James is about to puff away from Henry's Tunnel, if you listen closely, James is heard puffing before he has even left. (00:10:00)
The Sad Story of Henry - S1-E3
Revealing mistake: When the passengers try to pull Henry out of the tunnel, they have putty on their feet. Sir Topham Hatt's hand is also purple.
Edward, Gordon and Henry - S1-E4
Visible crew/equipment: When Gordon backs on to the siding, you can see the inside of his cab, which is just some equipment.
Edward, Gordon and Henry - S1-E4
Other mistake: When Gordon leaves the station, he has two brake coaches, even though express trains are suppose to have one.
Edward, Gordon and Henry - S1-E4
Other mistake: When Gordon is sent to the siding after breaking down, he passes the set of points needed to cross over to the other line.
Edward, Gordon and Henry - S1-E4
Visible crew/equipment: When The Fat Controller is looking at the goat, a hand is visible in the steam.
Edward, Gordon and Henry - S1-E4
Continuity mistake: When Henry comes out of the tunnel, he's dirty, in the next shot, he's clean.
Answer: He was in the water.