Another funny anecdote in that category I didn't see in the article is Isaac Asimov's novelization for Fantastic Voyage. Because of filming delays the book was published 6 months before the film release, leading many people to believe the film was an adaptation of the book.

That novelization differs significantly from the movie, but mostly because Asimov thought the screenplay was filled with bad sci-fi plot-holes and was given permission to change whatever he liked.