You're speaking solely about the film. The book goes into great detail about this.

That is not true. In fact the book was very clear how this occurred; I would have to rewatch but I believe the movie also hints at this. I thought the book's discussion of side pocketing was one of the most revealing parts of book: Lewis did an excellent job at explaining the recourses available to money managers.

Here's two short paragraphs from page 145 (of my copy, anyway) of The Big Short:

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> One night, as Burry was complaining to his wife about the complete absence of long-term perspective in the financial markets, a thought struck him: His agreement with his investors gave him the right to keep their money if he had invested it "in securities for which there is no public market or that are not freely tradable." It was left to the manager to decide if there was a public market for a security. If Michael Burry thought there wasn't--for instance, if he thought a market was temporarily not functioning or somehow fraudulent--he was permitted to "side-pocket" an investment. That is, he could tell his investors that they couldn't have their money back until the bet he'd made with it had run its natural course. And so he did what seemed to him the only proper and logical thing to do: He side-pocketed his credit default swaps. The long list of investors eager to get their money back from him--a list that included his founding backer, Gotham Capital--received the news from him in a terse letter: He was locking up between 50 and 55 percent of their money. Burry followed this letter with his quarterly report, which he hoped might make everyone feel a bit better.

...

> Immediately, his partners at Gotham Capital threatened to sue him. They soon were joined by others, who began to organize themselves into a legal fighting force. What distinguished Gotham was that their leaders flew out from New York to San Jose and tried to bully Burry into giving them back the $100 million they had invested with him. In January 2006 Gotham's creator, Joel Greenblatt, had gone on television to promote a book and, when asked to name his favorite "value investors," had extolled the virtues of a rare talent named Mike Burry. Ten months later he traveled three thousand miles with his partner, John Petry, to tell Mike Burry he was a liar and to pressure him into abandoning the bet Burry viewed as the single shrewdest of his career. "If there was one moment I might have caved, that was it," said Burry. "Joel was like a godfather to me -a partner in my firm, the guy that 'discovered' me and backed me before anyone outside my family did. I respected him and looked up to him." Now, as Greenblatt told him no judge in any court of law would side with his decision to side pocket what was clearly a tradable security, whatever feelings Mike Burry had for him vanished. When Greenblatt asked to see a list of the subprime mortgage bonds Burry had bet against, Burry refused. From Greenblatt's point of view, he had given this guy $100 million and the guy was not only refusing to give it back but to even talk to him. And Greenblatt had a point. It was wildly unconventional to side-pocket an investment for which there was obviously a market. There was clearly some low price at which Michael Burry might bail out of his bet against the subprime mortgage bond market. To some meaningful number of his investors, it looked as if Burry simply did not want to accept the judgment of the marketplace: He'd made a bad bet and was failing to accept his loss. But to Burry, the judgment of the marketplace was fraudulent, and Joel Greenblatt didn't know what he was talking about. "It became clear to me that they still didn't understand the [credit default swap] positions," he said.