Revealing mistake: When Mia meets Asana at her birthday party and asks what she's been up to, Asana replies "oh, partying girl" with a British accent. Then when Asana is talking about Prince Jaques, the accent is gone. Then, at the slumber party, her accent slightly returns.
Revealing mistake: It is quite noticeable that during the party, the "rising star of opera" is lip-synching. Her posture and mouth movements are not like that of an actual opera singer, and there are no visible vibrations of her throat when she sings.