Other mistake: In the panning shot of Percy, Gordon, and James, the Breakdown Train on the far left is derailed.
Thomas and the Missing Christmas Tree - S2-E26
Other mistake: In the shot of Donald, (or Douglas) Gordon and Henry, Donald has Edward's face.
Thomas Comes to Breakfast - S2-E18
Other mistake: The narrator said Thomas was feeling conceited, but Thomas had his sad face mask on instead.
Answer: He was in the water.