Other mistake: Hawkeye loosened the nut and locking ring, but after lifting the assembly, it was obvious that these were steps used only to heighten tension. There was no locking device of any kind between the tail and body of the bomb.
Other mistake: When Hawkeye walks into the shower tent while Ugly John's showering he removes his robe, and just as Hawkeye swings open the door to step into the shower stall we can see that he's wearing something, presumably a swimsuit.
Other mistake: While the dentist is working in Henry's mouth Frank's describing Hawkeye and Trapper's pranks, and right after we see a shot of the dog licking hamburger from Frank's ear, when it cuts to Henry saying, "Frank, just leave my married life out of this. Doc, will you watch it before I swallow your watch!" keep your eyes on Larry Linville as he mouths McLean Stevenson's lines along with him.
Other mistake: While celebrating the ceasefire, a Jeep full of people including Father Mulcahy stops between the Swamp and the main building. There's a streamer hanging down either side of Mulcahy from above the top of frame. Unless there's a power line to the Swamp that never appears at any time, there's nothing for it to hang from.
Other mistake: During this episode, Trapper and Hawkeye keep switching Frank's pistol with other things. When Frank's training his South Korean platoon, Trapper, Hawkeye, and Radar show up all decked out, and while Hawkeye's telling Frank that using the anti-aircraft gun on the compound will draw enemy planes, etc., there's a pistol in Frank's holster. When Frank turns around, we see that Trapper's right arm is bent over his fly swatter the entire time until he steps away from Frank, and when Frank draws from the holster what he believes is the pistol, he pulls out a plunger, and although it's funny, Trapper never actually had the opportunity to switch the pistol with the plunger, nor did Hawkeye or Radar.
Other mistake: Radar says the weekly report is for the 17th to the 22nd inclusive. A 6 day week in the middle of a war?
Other mistake: The Chinese patient cut the strap of Klinger's red gown, but Radar says Klinger requests a replacement brassier. Later Klinger's red gown shows no damage, although he could have retied the strap.
Other mistake: When Hawkeye and Trapper are arguing with Henry about not sending the little boy to the orphanage, Henry says, "Look, you think I wanna send this little fella away? I got two kids of my own. I'm a former child myself," but at the end of season 1 Henry's wife delivered a boy, whom Henry was aching to be with, so Henry really has three kids.
The Sniper - S2-E10
Other mistake: When Hawkeye and Trapper make Frank up to look like MacArthur, as they put the pipe in the "sleeping" Frank's mouth, he opens a bit wider, and bites down on the stem, then says his last line of the episode.
Hot Lips and Empty Arms - S2-E14
Other mistake: While trying to sober Margaret up, you can see Trapper's clothing wet in spots where she hung on to him in previous takes.
Other mistake: When Henry is trying to convince Baker how wonderful the camp is, Henry says that they "had 'The Thing' and 'The Blob' both in one week." The movie "The Blob" was made in 1958. This season of M*A*S*H is set in 1951 and 1952 (and the war ended in 1953). (00:03:55)
Springtime - S3-E6
Other mistake: While Radar is measuring the camp, he says that last year they had 2,986 square feet, but this year they have 2,863 square feet. The square root of 2,863 is about 53.5, so unless the camp is 53 feet by 53 feet (!) his numbers are WAY off. (00:16:15)
Mad Dogs and Servicemen - S3-E13
Other mistake: Hawkeye, Henry and Trapper are playing scrabble. The board is in an illegal state - in the lower right corner 'it', 'jot', 'joy' 'yearn' and 'in' are not connected to the rest of the words. Since the others call Hawkeye on his non-existant word, I'm assuming they're playing properly. (00:15:35)
Other mistake: When Trapper and Hawkeye are driving along, you can see two points of light on the steering wheel. The lights are from from the filming illumination panels.
Other mistake: When Trapper and Hawkeye make the right turn after Trapper tries to use the restroom, you see that Trapper avoids the left side of the road just after the turn. This is to avoid the explosive charge set in the ground used to simulate a mortar round exploding.
Aid Station - S3-E19
Other mistake: After Hawkeye gets back from Aid Station, Trapper is making a cup of tea. When he tries to hang the tea bag on a nail on the tent post, it unwinds and falls to the floor.
Suggested correction: This isn't a mistake, especially since we don't see it hanging back up in another continuous shot.
Other mistake: In the opening, when the flags were raised, the United Nations flag is hung upside down.
Other mistake: It's 1952 when Potter arrives at the 4077. He tells Radar that he joined the army during WWI when he was 15 (he lied about his age). That would mean that Potter was 50 when he arrives. But he said that he'd be retiring in 18 months. Also, in the episode "Point of View" Potter states that this was the first time in 37 years that he missed calling Mildred for their anniversary. That would mean that Potter was 13 when he got married.
The Late Captain Pierce - S4-E4
Other mistake: When Digger shows Hawkeye the copy of the death certificate, Hawkeye steps out of the shower stall and its door swings back and forth. As Hawkeye wipes his face with the towel, we can see the top of the flesh colored covering Hawkeye is wearing. (00:08:05)
Other mistake: As Burns, driving the tank, runs over the Swamp, there's no sign of the still anywhere.