Continuity mistake: At the track meet, Laurie runs the third leg of the 4x100 and hands off to Doris to run the anchor leg. At the finish line, Laurie is there to cheer on Doris as she crosses line first. Only the first and second runners of this relay would have time to make it to the finish line in time to see the end of the race.
Deliberate mistake: Fading is mentioned throughout the film. However, according to the director in the commentary, they don't really start to fade until the third time it's mentioned.