Look closely: EVERY time you see Hugh Grant entering his book-shop, there's a nice scene of a mother comforting her crying child at the background...not one time, but EVERY time.
I guess that child is quite depressed :-)
I'm not taking credit for this one, because I heard it from a friend, but this slip-up is- I suppose- a big mistake, isn't it ?
I don't think this is really a slip up but rather an "are you really paying attention" for movie enthusiasts that movie producers/directors sometimes slip in for added interest. Alfred Hitchcock did this by having cameo appearances in all of his films and in the movie Joe Versus the Volcano you will find a lightning bolt shape repeated throughout the film (in the walkway leading up to the factory, on the wall in his apartment and in an actual lightning bolt that sinks the Twiddle-Dee). If you look closely at the mother-daughter scenes you will notice that they are different each time, however there are similarities. In the first one there is a man walking behind Hugh Grant wearing a jacket tied around his waist who is also in the final mom-kid scene toward the end but isn't in the other. There is also a man walking right to left in the second mom-kid scene wearing a dark jacket with a white area on his left sleeve who is also in the last one but isn't in the first one. They were probably(?) all shot at the same time but they are different "takes"