Other mistake: In the 'Macavity' dance, Demeter makes a mistake with one of her moves and makes an "Oops." face.
Continuity mistake: At the beginning of the song "Old Deuteronomy" watch the positions of Jo Gibb and Drew Varley flip flop in the background between long and close shots. Soon afterward, Cassandra slides down to the stage in a closeup and immediately slides down again in the long shot (while singing different lyrics). Apparently the long and close shots were often filmed in different takes and the choreography and positioning of actors were sometimes not matched very well.