Deliberate mistake: As Christine approaches the Phantom in his lair (just after he has abducted her), we see that she is wearing very dark black eye-shadow. Back in the dressing room after coming off stage, as she talks to Raoul, we saw her face in close up and she was not wearing any eye-shadow at all, even though the Phantom leads her through the mirror just after she has managed to slip on a robe over her undergarments and she has not yet changed to go out to supper (Raoul says she is to be ready in 2 minutes). Her hair becomes 'bigger' and wilder, too. The change in her appearance is a reference to her descending (voluntarily, I might add - he didn't drag her through that mirror) into the Phantom's dark existence and to her sexual awakening. (00:28:45 - 00:37:10)
Deliberate mistake: Throughout the film, scenes of several Cole Porter productions are shown being performed. These scenes all contain a well-known musical number. Two scenes in particular (after the Alanis Morissette number and immediately after the "So in Love" duet) end with the lead singer/singers bowing to the audience and then waving the other cast members on stage to take a company bow. The problem is that neither of those numbers appear at the end of the shows being "performed." The "So in Love" duet, for example, most definitely appears in the musical "Kiss Me, Kate" well before the Act Two finale. I assume that these mistakes were filmed deliberately to emphasize the importance of the songs in question, but they are still errors.