When Jackson first discovers Miley sleepwalking, she falls into his arms. Her left arm ends up around his back. When they walk in the door, it is under his arm, but when the cut goes inside the house, her arm is on top of his instead of under. She's asleep, and she obviously couldn't have moved her arm.
When Miley is singing the new song, she is playing the piano but there is no noise coming from the piano.