Continuity mistake: Early in the episode a tank is driven into the MASH compound by a wounded soldier (demolishing the latrine in the process). The tank is an M24 Chaffee dating from the mid 1940s - it is squat and angular in shape. Later on in the episode after the tank has been hidden under a tent Hawkeye decides to drive the tank into the camp dump (demolishing the new latrine on the way). The tank has changed into an M4 Sherman - it is a lot higher and more rounded in shape.
Continuity mistake: When the injured tank driver appears in the open hatch while Margaret's yelling at him, he does not have a bushy mustache, but in the next shot in the OR we hear Margaret telling Potter about the tank driver while they're operating on him, and when the camera pulls in closer we see that he has a big bushy mustache. (00:10:50)
Continuity mistake: While everyone's gathered for their last evening together, taking turns telling what their life will be like when they get home, there are three closeups of Kellye in which we see that her caduceus insignia pin is on her right lapel and her First Lieutenant bar is on her left lapel, though it should be the opposite way, and her closeups are not flipped. The pins are on the proper side in other shots of Kellye during the episode.
Visible crew/equipment: While Klinger is on the phone trying to set up BJ's transportation home, just as Winchester walks into the office pointing out the company clerk the shadow of the moving boom can be seen on the wall, and it's also visible when Winchester takes the mailbag and dumps the contents. (00:42:50)
Continuity mistake: After Klinger presses Potter about getting rid of the tank Potter tells Klinger to act like a sergeant, and in the shot from Potter's office Klinger walks out with both of his helmet straps hanging loose, but when it cuts to him walking into the outer office one of the straps is suddenly gone. (00:33:45)
Continuity mistake: When Father Mulcahy releases the locked up POWs, in the following explosion Father Mulcahy is knocked to the ground and his eyeglasses are still on his face properly, but in the next shot when BJ rushes to his side the eyeglasses are on the ground behind Mulcahy's head, and BJ did not remove them.
Continuity mistake: When Hawkeye is returning to camp, he and his driver completely pass some Burma-Shave signs the other have set up to welcome him back. An ambulance bus is a few feet behind them and manages to then suddenly appear at least 30 feet behind them to smash all the signs.
Continuity mistake: B.J. is holding a Korean child who is subbing in for his own daughter when Margaret hands B.J. a piece of cake. Just as it looks as if he is about to feed the cake to the girl, the scene cuts to a full facial shot of Hot Lips, then cuts back to B.J. The cake has disappeared. There wasn't enough time to eat it all, and neither the child nor B.J. is eating. B.J. has no icing on his fingers; it has just disappeared. (01:16:50)
Deliberate mistake: BJ mentions to Charles that if they don't sign the armistice it will be the second time in 2 years and then he will miss his daughter Erin's second birthday. This is BJs 7th season and when he arrived at the beginning of season 4, Erin was already born, making it absurd that seven years later she could still be one year old. Because the real war lasted 3 years and the show 11, there are obviously some errors like this that can't be avoided but this was blatantly egregious.