Colonel, once you have commenced your FDP (signed on), the company can request you to use Discretion (7.2.1.1). Happened regularly with rest on one of the LHR patterns, and was common departing North America on the Jumbo.
Now it's not supposed to be "regular practice" - the grey area.....
I'm not sure of the exact details of the LAX flight in question, but if they signed on, then found out they were one short.....