The Crab with the Golden Claws: Part 2 - S1-E2
Other mistake: The newspaper article that features Tintin and Captain Haddock at the end of the episode is a flipped shot, as shown by the text that has been reversed. (00:43:35)
The Retainer - S1-E2
Other mistake: The gas chamber is destroyed when the dogs pull a chain that's attached to its front support but it somehow collapses from behind. (00:19:07)