When Bobbi and the boys first go to the diner, Bobbi takes off her ponytail and then clamps it back on. When she clamps it, the top is smooth, but in the next shot there is a clump of hair standing up that goes in and out of the frame. In the very next shot it's smooth again.
John goes to the dance club with his son Evan. As the camera enters the club, John's son Evan and his girlfriend are dancing in the crowd. In the next shot, they are sitting with John just getting ready to go out onto the dance floor.
When John and Miss Mitzi are dancing at Dr. Dance, they bump into Link and his dance partner. The dance partner has her hair covering her ear (down) in the wide shot, but in the closer shot, her hair is behind her ears.
When John and Link are heading out of the office on the evening of the final dance party, Link takes the escalator. Just before Link gets on, a gentleman talking on a cell phone does. The next shot from below, the gentleman on the phone has his hand in his pocket.
In the first ballroom lesson Miss Mizzie teaches standard slow waltz mirror-inverted: she teaches "left foot forward, right foot side, right close..." which are ladies 2nd part steps. Men's are "right foot forward, left foot side, right close".
A major plot point is John's realization during the dance competition that his wife and daughter are in the audience, meaning they have discovered his secret. However, the idea that Bobbie would hear someone in the crowd yelling "Go, Dad!" over the music and would assume it was John's daughter is preposterous. Even more preposterous is the suggestion that a couple in a dance competition would break their concentration to have such a frivolous conversation.