Revealing mistake: After Kelly tells Big Joe he's going after the gold "with ya or without ya", a soldier in the background walks past a steel tank trap weighing a quarter ton (http://en.wikipedia.org/wiki/Czech_hedgehog). He bumps it with his backpack, and it flips up in the air. (00:24:35)
Revealing mistake: When Oddball's tanks raid the train station, watch the two Germans with the MP 40s caught by the first cannon blast. When the explosive charge used for the effect goes off, they jump forward.
Revealing mistake: At the end of the scene with the destroyed bridge, when Oddball's Sherman drives away, Cowboy is nearly left behind and climbs onto the rear of the tank by standing on a box attached to the rear plating. The next time we see this tank from the rear, the box is gone. It was obviously there only to help Cowboy climb on.