Other mistake: Hawkeye reads the propaganda flyer, he says. "Give yourselves up, you can't win. Douglas MacArthur." Trouble is, the papers are all advertising for a flying company called Ace Eli.
The Trial of Henry Blake - S2-E8
Revealing mistake: As Klinger flies on his home made glider it's easy to tell that it's a bad composition shot. Also, nobody moving in the shot of him taking off stopped to notice him.
Character mistake: At the end of the episode, while Col. Potter is in the helicopter asking where they are, the pilot says they are about 10 miles west of Inchon. Col. Potter says this is no good and he tells the chopper pilot to "head west, towards Inchon." If they are already west of Inchon, heading west will take them further from Inchon.
Suggested correction: Potter tells the pilot to head to a different city, Chuksan (not sure of its spelling).