Revealing mistake: Episode Aired 12th December. In the laundrette a shelf had fallen off the wall and Dot Cotton needed someone to fix it. You could see the wall was false, as every time Dot touched the shelf, the wall was wobbling. Later same episode Martin Fowler fixed the shelf he said something like "the wall will fall down before the shelf does" - very true.
Revealing mistake: Episode 1720: When Todd is knocked down by the van, you can see that it is not Kristian Schmid but a stunt double.