Continuity mistake: There are two sets of the 4077 compound - the outside Fox Ranch set located at Malibu Creek State Park, and the second set inside the studio's Stage 9. The layout of both sets are quite different - Studio 9's set was vastly smaller than the Ranch set, so things such as the proximity of the Swamp to the mess tent are different between the shots filmed at the Ranch and shots filmed at Studio 9, when seen within the very same episodes.
Continuity mistake: In any scenes in the CO's office, look at the windows - they're sometimes opaque, sometimes clear. Also the windows in the OR. Usually semi-opaque, once, they were totally opaque, and made of a thick plastic. This was because it was very cold outside, and Hawkeye used a scalpel to cut them open to let in cooler air.