Other mistake: In the original version, when the Rebel Transport ship leaves Hoth before the ion cannon is fired, an X-wing flies past it, and you can see the transport ship through one of its wings. This has been fixed in the Special Edition.
Other mistake: In the original version, in the first wideshot of the Super Star Destroyer, on the right side of the screen, the light of a Star Destroyer (but nothing else of it) can be seen just flying through space for two seconds before it disappears. This mistake is fixed in the Special Edition.
Other mistake: When the Star Destroyers are seen for the first time, in the second shot, some of the TIE fighters that fly over a Star Destroyer are transparent.
Other mistake: When the Millennium Falcon escapes Hoth and is pursued by the Star Destroyers, frantic movements cause them to collide. Watch the interior shot of the Star Destroyer as everybody is thrown around. Near the bottom of the screen one of the computer consoles comes away from the wall and is hurridly pushed back into place by a controller! (00:35:55)
Other mistake: After Vader cuts through a pillar with his lightsaber in the beginning of the duel, the hole in the pillar is much bigger than it should be. (01:37:35)