Continuity mistake: When the Sarlacc tries to drag Lando into the pit, the tentacle is grabbing his ankle in some shots. In other shots, it is wrapped around his thigh as well. (00:33:50)
Continuity mistake: During the battle between Luke and Vader, their sabers alternate between casting shadows on the floor, and no shadows. (01:52:40)
Continuity mistake: In the beginning of Luke and Vader's lightsaber duel, and also in a few shots right after Luke knocks Vader down the stairs, Vader's cape alternates between being draped behind and over his left shoulder. (01:48:55)
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)
Continuity mistake: When Boba Fett falls into the mouth of the Sarlaac, he disappears just before the beak touches him. (00:33:45)
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 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 the shield generator explodes, a piece of shrapnel flies towards the left side of the screen and then flies back, because it bounces off the inside of the building the miniature was housed in. (01:50:05)
Continuity mistake: In the scene where Luke and the others are trapped in the net, the dead animal changes appearance (both injuries and actual appearance) and position several times. For example, the animal seen when they are in the net has a different mouth and a bigger area of white fur from the one seen a few shots earlier. (01:08:35)
Continuity mistake: When Vader throws his lighsabre, it hits one of the supports holding the catwalk, but in the next shot, it is nowhere to be seen. (01:45:50)
Continuity mistake: When Bib Fortuna attempts to persuade R2-D2 to show him the message to Jabba, his hands keep changing position between shots. (00:07:20)
Continuity mistake: When Lando says goodbye to Han, after Ackbar's speech, Lando's lapel pin/medal swiches shoulders several times. (00:51:40)
Continuity mistake: When Luke and Vader enter the Emperor's throne room, they walk towards the stairs, and as the shot ends, Luke put his foot on the first step. In the next shot, they have suddenly moved further up the stairs. (00:26:45)
Continuity mistake: Just after R2-D2 cuts the net that holds him, Luke, Han, Chewbacca, & C-3PO, you can see that before the Ewoks pop up out of nowhere to see their captured victims, one Ewok just stands there in plain sight waiting for the others to reveal themselves.
Revealing mistake: Widescreen version: After Luke cuts off Vader's hand, the Emperor says, "Now, fulfill your destiny, and take your father's place at my side." In the next shot, Luke's lightsaber blade goes through the railing, without damaging it. (01:49:15)