Continuity mistake: After Eugene takes the stage to face Jack Butler, everyone (including Eugene) turns when Scratch walks into the room. When Scratch sits down and Eugene turns back to face Jack Butler, Eugene's hat is gone.
Other mistake: When Eugene discovers that it really is Blind Dog Fulton, he (Fulton) says that he needs to get out to help Eugene find that lost song. Eugene says that he will be here at "5:00 a.m." When they breakout - which took all of about maybe 10 minutes, it's very light for the morning time. Looks to be maybe 6:30 by daylight savings time.