Other mistake: When the phantom sings behind Christine's mirror in her dressing room, she starts to walk towards it, entranced. It's obvious he is behind the mirror, and it's a one-way mirror. But, when she touches his hand, wouldn't the mirror have to be opened up? They act like she can just walk into the mirror. (00:30:55)
Suggested correction: When the Phantom begins singing behind the mirror and Christine approaches, it appears as if she walks through the mirror to the other side, then grabs the Phantom's hand. The hallway she is taken into is elaborate, with gold human arms holding candles. Later, when Meg looks for Christine in her room, she finds the mirror odd and slides it open to enter the secret hallway, finding it dark and rat-infested. This proves that what Christine saw was in her mind and that she imagined she walked through the mirror.