Re-thinking Convention and Innovation

The end of Ferris Bueller’s Day Off (1986) defies the conventions of film endings. After the credits are over, the music has stopped, and the screen has faded to darkness, we are suddenly confronted with an interior shot of Ferris Bueller’s (Matthew Broderick) home. Is this the start of a new movie? Did the film’s editors make a mistake and forget to remove some material from the final product?