Character mistake: When Tracy is about to announce that the wedding is off, she turns to Dexter for help, and he says "Two years ago..." Tracy starts the announcement "Three years ago..."
The Philadelphia Story (1940)
1 character mistake - chronological order
Directed by: George Cukor
Starring: James Stewart, Cary Grant, Katharine Hepburn, Ruth Hussey
Revealing mistake: In the scene where Cary Grant punches Jimmy Stewart: Jimmy starts falling back (and you hear the sound effect of the punch) when Cary's fist is a good 1-2 feet from Jimmy's face.
Sidney Kidd: You hate me, I trust, Miss Imbrie.
Elizabeth Imbrie: No, I-I can't afford to hate anybody. I'm only a photographer.
Trivia: Hepburn wanted Clarke Gable and Spencer Tracy for the male roles, but the studio gave her Cary Grant and Jimmy Stewart instead. (She did get Spencer eventually when requested for Woman of the Year).