Yep - Dave's definitey right on that one... I agree 100% - it's just the lining sticking out... no leather-edge [cape wouldn't drape right and there really is no purpose/need to protect the edge of the cape]... sloppy craftsmanship is the answer - as so often seems to be the case in the SW movie/prop-making universe.
woah hold on thats a huge jump in logic.

A shine can be created with a nice garment leather just the same as satin. Actually, some satins can absord light as well. I regularly buy leather and work with a leather repair fella. There are plenty of thin, flexible leathers that could create the same shine as """satin""" Lots of historical leathers were thin and covered armor. There shine was quite evident.
As for sloppy tailoring I find this a weaker argument simply because by ESB, the LFL budget was much bigger and Vaders costume was clearly overhauled. A crappy edge would have been noted in the ILM costume reviews in which the costumes were worn and the actors moved and posed to review the costume. A three or four inch overhang would have been caught, Im pretty sure.
....well, unless you're rock climbing with the cape on, a hemmed satin edge will hold up just fine.
try cement or many other urban environments...or sets that contain edges...
, the edge shown is very shiny...looks like a satin to me.....
you guys need to think about set-lighting. Its not the same as holding a piece of leather in one hand, and a piece of satin in the other and saying
a-hah, we have a shiny winner. Set lighting is essentially the dual between intentional light and shadow. Ive been on a handful of sets and done costumes attesting to this balance. I guess what Im saying is simply that while NONE of us can prove what the hell the edge was....
....it is going a bit far to assuredly declare it satin.
As for this photo...I suspect it could be a stunt cape. Very short.
That actually brings up a good point...given the sheer paucity of reliable photos, I think all this is rather moot.
My advice to anyone trooping, get a garment leather edge. DO NOT risk your expensive wool scraping---even every so often --- on the ground or an edge. If you spent all that money on a good cape, dont let it get scuffed. Unlike Darth Vader, most of us dont have two dozen capes in the
hypercloset.