Continuity mistake: Millie's beads have a mind of their own. They do not stay in place even when she is standing still. Besides the funny scene during the title credits (when it is deliberate), and when Miss Dorothy registers, they also move during a scene when Millie displays her thoughts on Miss Dorothy's beads when the two of them go into the elevator for the first time.
Revealing mistake: In the beginning when Mrs. Meers goes into the elevator, you can see that the elevator floor is a continuation of the room floor, just with a strip across it.
Revealing mistake: When Jimmy and Millie are sitting on the ledge of the building she works in, Jimmy leans forward, and the top of his head disappears - or actually fades into the background.
Continuity mistake: The elevator that Millie and Miss Dorothy use changes from an elevator to a small room with the walls of the building missing and the door as well.
Revealing mistake: Jimmy and Millie are sitting on the ledge of the building and stand up. When Millie is about to fall and waves her arms the left one becomes semi transparent and merges with the background.
Continuity mistake: When Mrs. Meers welcomes Millie for the first time, the position of her hands on the counter is inconsistent in every shot.
Continuity mistake: When Jimmy falls off the ledge, he falls backwards, slightly facing to our left. An instant cut later, he has magically turned 180° and is now facing our right, ready to safely grab onto the pole.
Revealing mistake: During all of Millie and Jimmy's flag pole scenes, and afterwards when they are sitting on the ledge, the people and cars on the street are motionless, revealing the matte painting.
Revealing mistake: During the flying scenes, the stagger wires of the plane flicker, giving the sense they appear and disappear because of the blue screen effect.
Factual error: The movie is set in 1922, but the women's clothes are more along the line of 1928, with a strong 1960's influence. For an accurate depiction of 1922 fashion, refer to Season 4 of Downton Abbey.
