Revealing mistake: When Leia and Lando are holding off the stormtroopers while Chewbacca and the droids escape into the Millennium Falcon, a stormtrooper comes running through the doorway. You can see the burn mark on his armour before Lando shoots him. When the trooper is shot, another trooper comes running through the door, also with a burn mark on his armour. Then Leia shoots another (or perhaps the same) trooper, and the burn mark is once again there before the trooper is hit (watch in slow motion). (01:44:20)
Continuity mistake: During the battle of Hoth, Wedge flies a full circle around the AT-AT walker and when the walker begins to fall, you can see the cable around its legs, but in a side view of the walker falling, the cable is nowhere to be seen.