Star Trek The Wrath Of Kahn Bloopers Page
Kahn Knew Chekov
Just after Kahn catches Chekov and the captain in his ship, he says you I don't remember, then says to Chekov, but you I remember I never forget a face, but the fact is in the episode Space Seed, Kahn never met Chekov, Chekov wasn't even in the episode. Chekov was in charge of security while onboard the enterprise so they would have met up in the confrence room after Kahn took the ship (since all the other senior officers were there), but he wasn't which leads me to believe he wasn't even on board at this time.

Transparent Station
Before Reliant stops by Regula, as Carol Marcus is talking the camera is doing a fly over Regula, if you look carefully, you can see the moon through Regula. In superimposition techniques of the time, to superimpose you would either have to have a black outline or make the image slightly transparent, the latter sacrifice is made here.

Ive Seen That Before
Regula 1 is actually a upside down version of the space station (the one housing Admiral what's-his-name) seen in Star Trek: The Motion Picture.

Kirks Uniform
While engaged in Spock's death scene, as the camera shots dart back and forth between them, Kirk's coat/vest keeps switching from pinned open to pinned closed.

Kahn’s Strength
When Khan picks up Checkov he has to obviously pull Checkov back to the ground.

Genesis Cave
If you notice in the Genesis cave, it shows the crew standing in there, but when it shows a shot of the entire Genesis cave, it's a painting! How do you tell? The waterfall is not moving!

Blood On Kirks Uniform
After khan's initial attack scotty brings in a person who has been injured. Right before he dies he grabs kirk's shirt and leaves a large blood stain toward the top of the collar, when kirk walks back onto the brige the blood stain has gotten smaller and has moved down quite a bit. I'm not sure but i think it moves to the left side at one point or another.

Damage To Enterprise
After the Reliant has attacked the Enterprise Kirk and Spock walk to see the damage on the display. According to the movie the Enterprise was hit only on the rightside, but in the display we see the somehow they were also hit on the left and on the saucer right next to the dorsal fin. Is this the case of the bouncing phaser blast or what?

Hull
When the Reliant is first shown and they are speaking of the lifeform on the planet, in one of the "dinoscanners" you see that the damage control shows the Constitution Hull, when the Reliant is nothing but a saucer.