Continuity mistake: In the scene where Katey and James are in his car after leaving La Rosa Negra, James locks the car door on the passenger side but after he makes a move at her, Katey opens the door without unlocking it.
Continuity mistake: During the dance scene where Katie and Javier dance in front of the white screen (with Katie's parents dancing in the film in the background) the straps of Katie's dress of her left shoulder are sometimes up, and sometimes down. In one shot Javier even pulls down the straps while they were already down in the previous shot.
Answer: Because they were singing revolutionary songs. And at that time was strictly forbidden.