The Harvey Girls (1945). It basically tries to be the story of three waitresses played by Judy Garland, Cyd Charrisse and Virginia O'Brien (with the emphasis on Judy. Natch.) Mid-way through the film the three decide to stick it out in the wild west even though it is...well, wild!
Then Virginia O'Brien disappears from the film. She's not even in the final wedding scene. Where did she go? Now, I realize its easy for today's audience to overlook this but in 1945 Virginia O'Brien was a very big star. Did they notice?
(note: I know she was preggie while filming but always found it odd that she just vanishes. maybe she was kidnapped by Indians and became an "Injun, Too!" Oh wait, that's another musical.)
"ubiquitous"