Other mistake: When Catherine breaks into Crown's house, her assistants immediately get to work on the security panel. When the first assistant touches the panel, it falls off the wall and he has to quickly push it back into place.
Plot hole: When Renee Russo was reviewing the tape showing the room with the painting to see who stole the painting, and the tape was blank because the heat generated from the suitcase hidden under the bench, why didn't she just back up the tape completely to see who put the suitcase there in the first place? (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: 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: 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)
Revealing mistake: During the catamaran sailing scene, the boat jibes and Brosnan leaps across the trampoline and starts grinding on an empty winch, with no line in it. (00:37:40)
Factual error: The Monet stolen by TC is credited as being the first painting in the Impressionist school, a clear reference to Monet's "Impression: Sunrise" of 1872. However, the painting shown during the entire film is "San Giorgio Maggiore by Twilight," a 1906 Monet painting.
Factual error: When the thieves are coming out of the Trojan horse, during a shot a pile of sawdust in a cone formation on the ground. This formation couldn't have formed since the thief was sawing a line in the horse, not drilling one hole. (00:09:05)
Revealing mistake: During the glider scene when they show the close up of Catherine's face with Thomas leaning over her from behind, waving his hands, if you look at her sunglasses you can see all the white screens, the camera crew, the reflection of his hands, etc. You can see this every time they show a close-up of them from the front of the glider. (01:06:00)
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)
Other mistake: When Thomas' keys are taken and copied, the name "Medeco" appears on the keys. The duplicating machine used is for standard keys and cannot be used for Medeco keys.
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.
Revealing mistake: At the beginning, when Thomas Crown is in his car, getting ready to get out and walk up to the museum, they show a close up of his wrist watch to set the time; it says 9:08 a.m. A few minutes later when he is sitting inside the gallery eating his breakfast croissant, if you look carefully at his watch, it shows 4:30. In various other shots, it also shows 5:25 and 6:30, indicating at least 2 hours spent shooting the gallery scene. (00:02:25 - 00:04:00)
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)
Plot hole: At the end of the movie when everyone is standing in the gallery looking at the painting now back in place (with the smoke and sprinklers still dripping) they notice that now there is a new painting missing, the one Thomas stole for Catherine. However, none of the other metal wall coverings open or move except for that small side one revealing the empty frame on the wall. This makes no sense why only that one would suddenly open and none of the others. (01:40:50)
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)
Visible crew/equipment: When Crown nearly walks into the lorry at the beginning you can see cables of sort in the left hand mirror from the shot inside the lorry. (00:02:50)
Factual error: The man in the security room, when watching the thermal video footage states that the thermal cameras needs a difference of ten degrees (or something like that), thermal cameras operate within a range of two degrees so it would have to be a fairly rubbish camera and that's unlikely, seeing how it's guarding a Monet and all. (00:28:45)
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.
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.