Cinderella

It was Richard Rodgers who wanted the Fairy Godmother (Edie Adams) to be a beautiful young woman, arguing that since she had magical powers, it made more sense - a concept that met with disagreement amongst the creative staff until the composer's view prevailed.

When performing the duet with the Queen of the reprise of "Do I Love You Because You're Beautiful?", Jon Cypher as the Prince, accidentally sings a line of the song that was meant to be sung by the Queen, played by Dorothy Stickney. This occurs after he sings the line "Do I want you because you're wonderful?" The camera shifts to the Queen and you can see her open her mouth to sing her line "Or is she wonderful because you want her?" but she remains silent when the Prince goes ahead and mistakenly sings the line from his point of view. According to the interview with Jon Cypher on the DVD release, he didn't realize that he had made the mistake of singing over Dorothy Stickney's line until it was too late, and because it was during a live broadcast, there was nothing either of them can do. If you listen closely, you can also hear that at that point, the orchestra has to catch up with Jon's singing to make up for the mistake.

Edited into Great Performances: Rodgers and Hammerstein's 'Cinderella' (2004)