The part in Barry Corvall's hair keeps changing from right to left during the film.
When Brenda is preparing to leave the outdoor cafe, her beer glass is 2/3rd full with a head. When she stands up, the glass is only 1/3rd full and the head has disappeared. Also, the beer bottles on the table change from being together to being separated by the bowl of pretzels.
The German soldiers' uniforms, though otherwise correct for the late 1930s, feature blank white armbands without the Nazi swastika emblems real German soldiers wore.
The establishing shot of the U.S. Capitol near the start of the film includes many 1930s era vehicles, but the scene is supposed to be taking place in 1916, shortly after the Black Tom munitions plant explosion.
George Bancroft is credited onscreen as Dudley Garrett, but radio announcer Wendell Niles introduces him as Donald Garrett.
Martin Kosleck is credited onscreen as Karl Mullen and shows a business card by that name, but he is consistently called Müller in the film.