When Chanel and her mom are putting on cold cream, it shows both of them. Her mom's cold cream disappeared between shots
When they are singing at the end of the movie, Chanel's jacket is zipped/unzipped between shots.
Aqua and Galleria are in fact cousins, based on the books. But in the first movie she calls her parents Mr and Mrs Garibaldi. This is referenced in the second movie when Aqua calls Galleria's mom Auntie Dorothea.
When Galleria's talking on the phone with Chanel, and her dad comes in for the second time, she presses the hold button on the phone, and when she gets back on the phone, she doesn't press anything but just starts talking.
In the opening song when Aqua's foot gets stuck, her foot changes position.
When Galleria is playing the piano by herself at school, it's obvious she really isn't playing. Her hands are moving way too slow for some of the parts and at the end, her hands are playing very low on the bass notes when the notes heard are in middle-low C range.
At the beginning when they are singing, Dorinda, Chanel and Aqua fall over, but Galleria is still singing when they all get up, one of them puts her hand on Galleria's shoulder, you can hear her voice but her mouth is not moving
Most of the "cheetah" prints worn by the girls are in fact leopard spots.
When the girls are performing "Cinderella" in the beginning of the song when they look upward towards the camera, you can clearly see Galleria mouthing "look up look up" to Chanel and then you see Chanel's head look up.