Continuity mistake: Luke tells Threepio to tell the Ewoks that if our heroes are not set free, that he will use his magic. If you look on the right of the screen, Artoo is standing untied, even though at that point in the movie he had not been untied yet.
Continuity mistake: When Lando says, "Fighters coming in," a whole bunch of TIE fighters come towards them. There's initially a lot anyway, but then after about a second, two horizontal lines of 4 fighters appear from nowhere (centre screen, underneath the Super Star Destroyer). They suddenly just pop into existence, large enough that we should have seen them approaching. (01:31:20)
Revealing mistake: At the beginning of the ground battle on Endor, two stormtroopers are knocked to the ground by the Ewoks. In the following shot, one of the troopers has a big crack in the left shoulder of his armour. The crack was obviously not there in the previous shot. (01:34:40)
Deliberate mistake: The shots of the prisoner skiff during the transport to the Sarlacc Pit are reversed. This can, for example, be seen as Chewie's bandolier is on the wrong side, and that Han's shirt is overlaying the wrong way.
Continuity mistake: When Luke wedges the bone into the Rancour's mouth, in the first shoot from behind, he holds the bone horizontally. In the beginning of the next shot, it is pointing upwards. (00:25:25)
Revealing mistake: When Vader throws the lightsaber at Luke and the platform collapses, the point where the platform's columns connect to the ceiling have expanding circles of smoke coming from them as the columns detach from the ceiling, created by the charges used to sever the platform. (01:50:20)Vader47000
Revealing mistake: During the speeder bike chase scenes, speeders bikes don't affect any vegetation, even though they're flying near the ground at incredible speed.
Audio problem: When the Death Star is about to explode, Admiral Ackbar says, "Move the fleet away from the Death Star.", but his lips don't move. (01:57:30)
Revealing mistake: When Luke leaves the Death Star in an Imperial shuttle, a large girder or something falls right in front of his ship. If you watch closely, you can see it bounce, revealing the miniature. A huge, heavy girder wouldn't have bounced like this.
Continuity mistake: In the first shot of Chewbacca when he is in Jabba's dungeon with Han, his bandoleer is on the wrong side. (00:21:25)
Continuity mistake: When Han enters the cockpit of the shuttle Tyderium, as the shot ends, he is about to walk past Luke. In the next shot, he has already walked past him and has begun to sit down. (00:50:25)
Revealing mistake: When Luke is being fed to the Rancor, in Jabba the Hutt's dungeon, there are black outlines around the beast's legs, from the composite's blue screen special effect. This was edited out in the special edition rerelease.