Continuity mistake: When Stuart is on the phone with Kate and tries to explain who Leopold is and why he is with him, the clock on his wall moves back by about two minutes when she sits down. (00:13:25)
Continuity mistake: In the first heated discussion between Leopold and Stuart a pen suddenly appears behind Stuart's right ear. (00:17:15)
Continuity mistake: When Leopold leaves the apartment with Bart, the leash roles itself up in several loops between shots. (00:23:20)
Continuity mistake: When Bart lays a turd at a tree, the leash is wrapped tightly around the trunk holding him back, but after he is done he moves on forward, while the leash disappears at the top of the frame. (00:25:00)
Continuity mistake: In the board meeting scene in which the margarine commercial auditions are first being looked at, the video gets paused on the first man auditioning and then the second man auditioning, but in each subsequent shot of the television, it's back to being paused on the first man auditioning. (00:29:49)
Continuity mistake: Hector, the little boy who spends his afternoons at Stuart's place watching TV, is eating from a bag of 'pirate booty' in his lap when Leopold sees him. When he offers Leopold some, the bag is suddenly next to him on the sofa. (00:31:10)
Continuity mistake: At the dinner at Kate's Charlie stands up to prove his manners. His fork is empty, but when we see him standing there's some food on it. (00:37:20)
Continuity mistake: During the dinner at her place Kate has both her sleeves pushed up to the elbows, but after she takes some dishes to the kitchen there's one brief shot from behind where the right sleeve is pulled down. (00:37:40)
Continuity mistake: In the hospital Stuart tries to grab his neighbor's phone. When he detaches him from his life support and alerts the nurse he holds the receiver in his right hand. The camera changes to a shot from behind, and he picks up the receiver again with his right hand. (00:39:50)
Continuity mistake: When Leo and Charlie are on the street talking (just before they interrupt Kate's dinner with JJ), Charlie has a cell phone and napkin in his hand, but from one angle it disappears, then reappears in the shot (from a different angle). (00:56:20)
Continuity mistake: When Charlie and Leopold are walking home after they go to the bar, Leopold says it is after midnight and they should go home. The next scene is back at the restaurant with Kate and J.J. When the camera is on J.J., you can see his watch and it says it's 9:30. (00:57:00)
Continuity mistake: When Kate comes back home after the punctured dinner with J.J., her hair is freshly done. Even if she had ample chance to do this, it's out of the question that the rather messy style she had chosen for the dinner was not intentional on such an important occasion, and there was no reason to change this afterwards. (01:00:25)
Continuity mistake: Leopold tells Kate that by his 30th birthday he had "become a blemish on the family name", meaning he must be at least 30 in 1876, making his birth year at least 1846. When he goes forward in time to 2001, he is said to be at least 148 years old, making his birth year 1853 (2001-148) which would make him 23 years old. (01:11:45)
Continuity mistake: When Kate is on the top of the roof with Leopold eating dinner, you can see her dress has straps on her shoulders. When the camera shoots back and forth from Kate to Leopold, you can see that the strap has fallen off her shoulder and shows her bra strap. However, when they go back to Kate it is back on her shoulder. (01:12:00)
Continuity mistake: When Kate tells Leopold that her Sundays are spoilt because the day after is Monday, she cuddles herself against his chest twice in successive shots. (01:21:10)
Continuity mistake: When Darcy and Kate are in the office when Kate is getting ready to go to the party for Farmer's Bounty, Darcy is supposed to press the elevator button, but in fact she presses a spot right next to it. (01:40:05)
Continuity mistake: In the close up shot of Kate holding the photos during her acceptance speech, the hand holding the photos is a man's hand. (01:46:32)
Continuity mistake: When Kate appears in 1876 New York, including at the ball, she is wearing a different gown to the dress she was wearing in modern day New York. (01:51:18 - 01:53:10)
Continuity mistake: At the end when Kate arrives at the uncle's house, Otis says "what seems to be the problem?" The doorman looks up at Otis, but the very next shot is Kate and the doorman is looking at her. (01:51:50)
Continuity mistake: Toward the end of the movie when Leopold is making his speech of who he is going to marry, there is a shot of the crowd in the room. In the very back there is a person that runs in and stumbles about. Then there is a close-up shot of Kate coming in and stumbling around the exact same way. (01:51:55)
