There’s a section of an interview with Peter Bogdanovich from Peter Tonguette’s Orson Welles Remembered, which gives a pretty good indication as to why the relationship between Welles and Bogdanovich had, by the early 80’s, become ‘poisonous’, as Joseph McBride puts it. As Bogdanovich relates it, Welles, who had had a hand in the screenplay for Bogdanovich’s 1975 film Nickelodeon, was offered an acting part in the film too, the part eventually played by Brian Kieth. But Welles wanted too much money, and even though Burt Reynolds and Ryan O’Neal both agreed to forego part of their own salaries in order to satisfy Welles’s demands, Welles refused to let them do it when he found out about it.
Jump ahead four years to the production of Saint Jack, which was to be directed by Welles, and produced by Bogdanovich, Cybill Shepard, and Hugh Hefner. Shepard had been given the film rights to the novel as part of an out-of-court settlement with Playboy over the unauthorized publication of nude photos of her. As Bogdanovich says, the only reason why Shepard agreed to the settlement was so she could get those film rights for Orson to direct another picture in Hollywood.
Orson wanted the lead role to be played by Jack Nicholson, so with great effort and difficulty, Bogdanovich and Hefner were able to persuade Nicholson to break his existing contractual obligations and play the part. But then, just as they were getting ready to finalize the contracts with Nicholson, Welles suddenly changed his mind and decided he wanted Dean Martin instead. A furious and humiliated Bogdanovich then had to go tell Nicholson that Welles no longer wanted him. At this point, Hefner began having second thoughts about Welles directing the picture. The film was eventually directed by Bogdanovich himself, which reportedly angered Welles very much. The title role was played by Ben Gazzarra. If this story is true - and I see no reason to doubt it - it is unfathomable why Welles would want Dean Martin over Jack Nicholson, and it also indicates a possible reason why Nicholson, a few years later, turned down Welles’s offer of the lead in The Big Brass Ring.