Continuity mistake: The number of plastic self-adhesive stickers attached to the left side of the contract change. After the contract is flopped onto the table and just before Crown signs it, the first side view (very quickly) shows 3 stickers attached to the left side of the paper with red on the bottom. Crown pulls the pen from his jacket. No one touches the contract. The second view shows 2 tabs attached at the same place with red on the top. (00:00:08 - 00:07:58)
Continuity mistake: When he first sits in the museum, his watch shows about 4:30. Next scene, as the truck pulls into the museum, the clock on the right wall shows either 1:30 or 6:05. Next scene as he walks into the office and says good morning, it's shortly before 12 noon. (00:02:29 - 00:04:00)
Continuity mistake: In the opening sequence, when Crown decides to walk and has "Jimmy" meet him at the office, he is almost run down by a truck. First of all, the truck has to skid to a stop, yet there is a car no more than ten feet in front of it when they change camera angle. Why was the truck going so fast in the first place. Secondly, when Crown motions for the driver to pass, the same car is still stopped directly in front of the truck, yet the truck speeds off in a way that it should smash into the car in front of it. (00:02:45)
Continuity mistake: In the first scene in the gallery when TC is admiring the Haystacks painting, he is preparing to eat a croissant. In the shot looking at him face on, he maneuvers the croissant into position in the bag it is in, so that he can begin to eat it. However, in the next shot - a longer distance profile shot - just after he answers Bobby's question, he is already chewing on a mouthful and starting to tear another piece off. (00:04:00)
Continuity mistake: When the "thieves" are preparing the impressionist wing and inform Thomas Crown that the exhibit is closed, Crown responds with "It's only a quarter to five". Shortly after when the surveillance footage from the time of the robbery is being reviewed, the time stamp on the monitor says 5:54. I doubt that the whole robbery took 1 hour 9 mins, when the time in the movie was around 3 minutes. (00:17:40 - 00:28:30)
Continuity mistake: When TC steals the Monet, he places the painting in the briefcase and closes the case breaking the frame in half and thus ripping the edges of the painting. When at home he opens the briefcase and the frame is obviously crooked but when he holds the painting up to place it above the fireplace it is perfectly intact and the painting is not damaged. (00:20:10 - 00:22:30)
Continuity mistake: When TC opens the briefcase to steal the Monet, the thumb of his latex glove is ripped wide open, which would leave fingerprints. After he places the painting in the briefcase, the next shot shows him closing the brief case and the glove has magically repaired itself. (00:20:10)
Continuity mistake: When Crown returns home straight after stealing the Monet, the high external shot shows him open the door with his left hand. In the next internal shot he is opening it with his right hand. (00:21:25)
Continuity mistake: Thomas Crown comes into the police station to identify the thieves. As he is getting ready to leave, Catherine eavesdrops on his conversation as she fixes herself a cup of coffee. She then watches him out the window, drinking her coffee, as he runs to his car. The paper coffee cup changes from a purple swirl design with a little bit of green to a blue and white, geometric border with what appears to be an Asian design. (00:32:30)
Continuity mistake: During the scene when Thomas Crown is sailing, you can see the weather change from very dark and stormy, to just cloudy, to blue sky and sun, depending on the shot. (00:36:30)
Continuity mistake: When Thomas and Catherine are having breakfast and his servant Paul brings Catherine's special "green" drink, it changes colors. When Paul has it on the tray and sets it down on the table, it is a very deep olive green. When she goes to actually drink it, it's now a light pastel turquoise blue color. (01:02:20)
Continuity mistake: When TC and Catherine Banning are having breakfast together at TC's house, Paul brings Catherine her green shake to drink. In one of the first shots, the glass is only about two-thirds of the way full, however, in the next shot, when she goes to take her first sip of it, the glass is almost filled to the top. The color of the green shake also changes slightly. (01:02:25)
Continuity mistake: When they land in Martinique, and are on the airstrip loading up the vehicles, their luggage and the painting go into the second vehicle, a shiny black jeep. However, when they show the aerial shot of them climbing the mountain to Crown's house, the jeep is now painted in camouflage colors. (01:08:10 - 01:08:55)
Continuity mistake: In the glider scenes, the shots from the front show the sighting window in the canopy placed on the right side of the glider. But in the shots from the side, it is correctly placed on the left side.
Continuity mistake: When Crown's attempting to repeat his golf shot, he flattens the ball into the sand. Then when we see the club hit the ball, suddenly it's on top of the sand.
Continuity mistake: The Jeep and Cobra Mustang are shown covered in mud as they climb the hill to the house in Martinique, however when they arrive at the top, they are clean again.
Continuity mistake: In the scene at the of the movie where Catherine is whispering in the ear of Thomas, you can see that the ear is not from Thomas. Compare the ear with earlier scenes and its clear this must must be someone else.
Continuity mistake: The theft occurs on one of the hottest days of the year, as pointed out by the guards. When Katherine arrives that night, she is wearing a coat. The investigation lasts a week or two, and throughout that time, they wear jackets and even top coats. Katherine's breath is frosty in the air a week or so after the theft. The weather apparently went from really hot to really cold in a week or so - NY weather may fluctuate a bit, but not to that extent.
Continuity mistake: In the glider scene, Thomas Crown's watch switches back and forth between his right and left wrists.
Continuity mistake: When Renee is sipping coffee and watching Thomas Crown far below on the street running to his car, in her first look, the car is parked at a 45° angle headfirst against a rounded curb with two police cars to its left, but in the second snippet, when she looks, his car is parked across a street, as any car would be parked and with a sidewalk to its right. The rounded curb scene and the two cop cars are gone.
Answer: I believe that the Monet that Crown hides in his study is not the one that was stolen, it is a copy that he already had prepared. He can enjoy the copy knowing that the original (with the broken spreader bars) is also in his possession. The stolen original then goes to the forger who repairs the broken spreader bars, and then paints another painting (using water soluble paint) over the Monet, so he can "return" it to the museum 3 days later. It gets more complicated when he discovers that Russo is on to him so he has a second forgery made (even the edges forged to match) over the top of "Dogs Playing Poker." He doesn't know if it will be necessary, but given his research into his new adversary, he concocts this contingency. It is likely that he has many contingencies in place, but the "Monet with a ghost underneath" is the only one we get to see. Of course for my theory to hold water, there must be (or have been) that earlier forgery - unless it has been destroyed.
It's not the forgery that he takes out of the briefcase. Even if it were, he still put the Monet in the briefcase at the museum and would have had to break the frame to close the briefcase, thus also breaking the paint and tearing the canvas. The real answer is that it is just something that couldn't really happen, and the movie people don't want the viewer to notice.