The Ordeal of Israel Boone - S4-E2
Other mistake: When Daniel starts to fall down the hill when he is sick from the snake bite, there are two pick up trucks parked down on the road, a white one and a blue one. They show up on the right side of the screen.
The See-Paris-and-Die Affair - S1-E22
Other mistake: Solo seems to forget just who called whom when he calls Illya on the communicator. After Illya picks up, Solo answers as though Illya had called him instead. (00:32:40)
Attack of the Tree People - S1-E19
Other mistake: The captain of the ship that picks up Race and Dr. Quest talks with a German (and sometimes French) accent but the commands he gives are in Dutch, like "Volle kracht vooruit" and "Pik de drenkelingen op" (the Dutch accent is very different from the German accent, as is Dutch from German).
Other mistake: One of the natives putting the captured Seaview personnel into the cave is wearing laced up sneakers. (00:36:25)