Continuity mistake: When BJ is letting Hawkeye in on the fact the he was the only real victim of the gag, he's putting a forkful of eggs in his mouth. After the camera cuts to Margaret and back, he doing it again. His mouth was empty both times.
U.N., the Night and the Music - S11-E10
Continuity mistake: When Col. Potter runs out of his tent to say goodbye to Capt. Lal, he wears only one slipper. When the jeep drives away and Potter's feet once more are visible, both feet are in slippers. (00:22:05)
Goodbye, Farewell, and Amen - S11-E16
Other mistake: When Hawkeye drives the damaged tank out of the camp, the front MG is missing. There's not a mark on the armor surrounding the MG port that might suggest it was destroyed in battle. Why would a tank in combat just be missing one of its MGs?
Goodbye, Farewell, and Amen - S11-E16
Factual error: When Hawkeye leaves the tank after parking it in the trash heap, he comes out of the cupola hatch. He should be coming out of the driver's hatch, because he sure as hell didn't drive that tank from the turret.
Goodbye, Farewell, and Amen - S11-E16
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)
Continuity mistake: After the files blow up, Klinger sees BJ looking at them. If you look carefully, you see that his head changes position between shots.
Continuity mistake: When filming Hawkeye, BJ and Charles in the swamp before they go to Potter's tent, the camera has a clear, unobstructed view of the inside. When it pulls back you can see the end of the tent, but without the netting normally there.
Continuity mistake: When BJ comes out of the building and meets Paul, you can see a chain-link fence in the background that you never see any other time in the series.
Goodbye, Farewell, and Amen - S11-E16
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.