Originally, an adaptation of 'The Cradle Will Rock' was supposed to be filmed in 1984. Amy Irving and Rupert Everett were already cast in their roles and was supposed to be filming in Rome when the production fell apart.
At the beginning of Hallie Flanagan's Senate testimony, the court stenograper's machines are not operating although they are pressing the keys. Later in the scene, the machines are working properly.
The Diego Rivera mural, as depicted in the film, is not his original Rockefeller Center version design (for which in-progress photographs exist), but of the smaller re-creation Rivera did a year later in Palacio de Bellas Artes in Mexico City. The Rockefeller Center mural was larger, whereas the spatial arrangement of features in the re-creation (and in the film) is more compact.