Maybe it's the hand they cut off Luke.
When our heroes are placing the charges on the Endor bunker, there is a closeup of a gloved hand sticking an explosive to a surface. Then, when the general shot comes back, you can see that no one inside that bunker is wearing that type of gloves!

The Incredible Moving Chopped Hand.
Contributed by Stingr2001
During the speeder bike chase, check out how Luke's gloved hand, the one that replaces the cut-off one, moves from left to right a few times.

Maybe it's polyester!
The gang is captured by Vader and Han is going to be used as a guinea pig to test the carbonite freezing process. There he is, with his plain white shirt and his trusty black pants when...wait! Check out a very short closeup of Harrison Ford's head and shoulders where he appears to be wearing his jacket!

Polyester again?
I know everybody is asking this, if Han's hands where handcuffed when he is lowered into the carbonite freezing chamber, why is it then that when they pull him out frozen his hands are up? (Note: Apparently in the widescreen version Han gets his hands uncuffed but this is lost in the "cut up" television version).

A New Hope ~ Return of the Jedi