When Katie and Hubbel are meeting the group shortly after President Roosevelt dies, she makes her "meeting up every 5 years" comment, after that she says to Hubbel "What are we doing here?" When she says that, her lip movements don't match what she's saying.
At the beginning of the movie, Katie walks into a bar with Bill. They agree that Katie will have her usual, Dubonnet on the rocks. Bill disappears for a moment, then returns with Katie's drink, which has absolutely no ice.
At the end of the movie, Barbra Streisand and Robert Redford embrace. He's wearing a trench coat with the collar up. In the course of the embrace, shot from behind Redford, Streisand's gloved hand moves down the back of his head, ultimately flattening the collar of the trench coat. In the next shot, face-on to Redford, the collar of the trench coat is back up.
At the very end of the movie when the camera is behind Katie as she reaches up to touch the front of Hubbell's hair, he grasps her wrist with his right hand. When the shot immediately switches to behind Hubbell, his hand is not on her wrist.
Near the beginning of the movie, as Hubble is dancing with Katie, you can see her pearl ring on her finger go from the pearl centered on her ring finger to the ring turned and the pearl is down next to her little finger. The pearl is then centered again on her finger. It also looks like the ring changes size from fitting her snugly to being loose then fitting snugly again.
(at around 1h 10 mins) When Hubbel is at Katie's apartment, he thumps the frame located close to the window and places both hands on his hips. In the next shot, Hubbel's left hand is placed on the frame.
At the beginning of the film when there is a montage that depicts how athletic Hubbell Gardner is, there a shot showing a birds eye view of him throwing the discus. He throws the discus out of the throwing circle traveling from one side of the circle (9 o'clock) and sees him release the discus at the other side (3 o'clock). The correct position for releasing the discus is clearly marked on the circle at the 12 o'clock position.
In the opening scene, where the movie marquee is shown displaying Counter-Attack starring Paul Muni and Larry Parks - that film wasn't released until April 1945. However, The Way We Were starts in the spring of 1944.
In California, Katie is holding a "hot" pot and offers it to Hubble. He takes a spoonful and notes that it is, indeed, hot. However, moments later, Katie is holding the bottom of the pot with her bare hands.
In Katie's apartment the first time Hubbel visits, Katie prepares hot water for coffee. As she leaves the kitchen, it is clear that the top of the kettle is on crooked. As she enters the bedroom where Hubble is sleeping in the bed, the kettle starts to whistle which startles Hubble. The kettle would not have whistled with the top lop-sided.