Deliberate mistake: When Peter and Miraz are fighting, Peter stabs Miraz and then brings the sword back up for the killing stroke. There is no blood on the sword. This is deliberate on the part of Disney, so as not to show blood, but a mistake nonetheless.
Deliberate mistake: When Max and 99 are in the air, they can be seen talking to each other. This is not possible (as proven on Mythbusters) even if you were yelling at the top of your lungs. The wind would make any noise unrecognizable, yet we hear them talking to each other just fine.
Deliberate mistake: When the Dragon Emperor is giving his Terracotta army the speech near the end, you see a shot that pans across the faces of several of his soldiers. A few shots later, this exact same shot is played in reverse. It is very easy to tell if you look at the way the camera moves up and down to catch the different faces.
Deliberate mistake: The helicopter camera shot of buildings under construction in Dubai plays backwards, to achieve a better effect. It's given away by the traffic on the ground traveling backwards, trucks make this particularly obvious.
Deliberate mistake: When Zohan and Phantom are seen on the Palestine beach competing about which one is the tougher, they let themselves get bitten by a piranha to prove their point. While piranha are by legend very vicious fish, its presence here is a two-fold mistake, for a) piranhas are found in South America, and b) they are fresh water fish. (I know that this is for pure humour, but the writers should have picked a rabid crab or something; that would be more appropriate for the setting.).
Deliberate mistake: When Ami's school friend is killed, a short sword is stabbed into the top of her head. Less than a half-second later, we see her face is totally coated in blood, and she gurgles even more blood before dying. There simply has not been enough time for such a volume of blood to have dripped down her face.