Another textbook example: "Cat People" is a moody supernatural horror movie. The sequel, "Curse of the Cat People" is a poetic fantasy about a child's vivid imagination. The movies share a few cast members and supporting characters, but there aren't even any cat people in "Curse," which isn't remotely a horror movie!
As I understand it, the studio demanded a sequel to "Cat People," which had been a big commercial success, but the producer, Val Lewton, wasn't interested in repeating himself, so he made this delicate, somewhat arty movie instead--under the studio-mandated title, "Curse of the Cat People."
(Both films are very good, btw, but completely different in tone and subject matter.)
Oh, a bit of trivia: "Curse" was, I believe, the directorial debut of Robert Wise, who went on to direct "The Day the Earth Stood Still," "The Haunting," "The Andromeda Strain," "The Sound of Music," "West Side Story," and, of course, the first "Star Trek" movie.