Other mistake: Grammy says she was knocked up when she wore the wedding dress in 1929. She is celebrating her 90th birthday. That would have made her about 10, since the movie was made in 2009.
Other mistake: When Margaret and Andrew first walk into the Immigration Office there are a group of extras seated directly to the left of them, in two rows. One of them, a guy with glasses and long black hair, wearing a white shirt with patterns (back row, second from the wall, next to the guy in the light yellow shirt), briefly looks at the camera as Margaret and Andrew walk by.
Continuity mistake: In the scene where Magaret is talking to her two bosses, when Andrew knocks at the door, the boss who is on the chair adopts two different positions while listening to her. But he can't within such short time. At first his left hand is pointing at Andrew, showing Andrew not to interfere. Then just after, you can see him on his chair with his legs crossed. Then he returns to his previous position. (00:10:10)
Continuity mistake: When Gammy enters the bedroom on the couple's last night, after separating the two lovers, she walks away and nearly disappears in the corridor. Just after, in another shot, you can see her walking away as if she was still in the doorway, although she has already walked past it. (01:20:45)
Other mistake: When Margaret is hoisted from the water, her clothes should have been sopping wet, but they looked like they had partially dried over the course of several takes.
Revealing mistake: When Margaret falls from the boat, she is floating with her shoulders well above the water, probably due to a hidden flotation device. Her outfit was too tight to trap any air for buoyancy, and a fully clothed person would normally be up to their neck in the water.
Continuity mistake: In the scene where Margaret says "I know Frank can be scary to deal with." we see an over-the-shoulder view of her, with Bob's hand holding his glasses in the foreground. The shot changes to focusing on Bob, and the same hand is now on the desk. It was too quick to move.
Revealing mistake: During the scene in New York City when Margaret proposes, a Boston police car is quite noticeable in the background. (Filming took place in Massachusetts, not NYC.)
Other mistake: When Andrew and Margaret leave the immigration office, and they are standing outside talking, there is a short woman in a light green sweater that walks behind Margaret, repeatedly - either the backdrop is a greenscreen on a loop or they just had the extra making rounds behind the couple.
Continuity mistake: After leaving the immigration office, Margaret and Andrew are talking outside standing on the sidewalk. During the shot of Margaret, there is a person standing behind her to the left wearing a grey outfit. Next shot goes to Andrew, then back to Margaret and the person is gone. Next shot goes to Andrew, then back to Margaret and the person is there again.
Continuity mistake: When Andrew and Margaret are in the boat and Margaret is driving, her hair is blowing back in the wind except for one shot when she is "talking about his family loving him and he has Gertrude". Then her hair is straight down, when it should be blowing in the wind as the boat is speeding across the water.
Continuity mistake: At the end of the movie when Margaret is cleaning out her office, her hair has suddenly grown to the bottom of her waist. Throughout the movie it was just past her shoulders.
Continuity mistake: When Margaret answers Frank's call on their first night she bumps her bag off the chair. The bag lands on its side, the camera is then on Andrew, and when it goes back to Margaret the bag is placed neatly next to the chair.