Hunted killer Robert Miller Barr--whose companion was lynched in Yreka, California, the year before for killing two cops while he himself escaped--got a job as an extra in this movie while on the run. He appears in eight scenes. See "The Spokesman-Review", Sept 16, 1936.
According to Louis B. Mayer biographer Charles Higham, Nelson Eddy was reportedly so jealous and insecure about potential competition from tenor Allan Jones that he asked that Jones' footage in the film be reduced; the studio agreed and cut what would have been Jones' only solo number in the film, the famous aria "E lucevan le stelle" from Giacomo Puccini's "Tosca".
MGM's original intention was to film in Technicolor and to star Grace Moore. If these plans had gone through, this would have been MGM's first feature-length Technicolor film. However, Moore decided to pass on the film, Jeanette MacDonald was cast, photography switched to black-and-white, and this film became one of the biggest musical successes in MGM's history.