In the boardroom scene at the end, when Linus is standing in front of the window, Harborside Terminal in Jersey City is visible. Once he leaves the room, this very large building disappears from the background.
Near the beginning of the film, when Linus is explaining his plastic to David, he holds a lighter to the piece of plastic and brags that it cannot scorch. However, as he turns the plastic over, a giant black spot is visible where the plastic was scorched. In the next shot, the spot on presumably the same piece of plastic has disappeared.
When Linus and Sabrina start to dance in the indoor tennis court, each is holding a champagne glass. The doctor takes David's glass. In the next shot Linus and Sabrina are dancing and their glasses are gone.
After Sabrina tells Fairchild that the moon is reaching for her, we see a shot of the moon through the trees at the Larrabee party. Directly above and to the right of the moon, you can see the strings and holes of that backdrop.