The 1968 American independent horror film, Night of the Living Dead, is (apparently) in the public domain… but the stories of how it got that way range from the age of the film to how he neglected to renew the copyright to "it's not really in the public domain".
The "age" argument doesn't seem to hold water; I can't (for example) broadcast Disney's Snow White (a much older film), nor was Walt Disney Pictures able to adapt the 1939 Metro-Goldwyn-Mayer film The Wizard of Oz unencumbered.
So what's the status/story of the trademark and copyright of the "Living Dead" movies?