As you should know, for the Special Edition's Cloud City sequences, ILM added more realistic (CG) extrior shots. One such shot is when Lando is escorting Chewie, Han and Leia to a room for some "refreshments". ILM modified an existing window from the 1980 version by leaving a small portion of the original window intact, but also adding a CG exterior shot of an elevator which asecends as Han, Chewie and Leia walk past. If you compare the Special Edition and the original 1980 version, you will see what I mean.
In the SE, the group walk past this new CG window and down a small set of stairs. They walk directly forward to a closed door which Lando opens to reveal Darth Vader. Now, look carefully here because the shots are quick at first. There is a camera shot taken from behind Vader which reveals Han in the doorway firing his blaster to no avail. Look behind Han in this shot and you will see the set of stairs they came down to reach the room and also a very retro looking glass window - the exact same window from the original 1980 release!
If you need a better look, just wait a couple of seconds until after Vader says "We would be honoured if you would join us" when in run the Storm Troopers down the stairs directly in front of the original and now unmodified window in a nice revealing wide shot.
Whoops! In an attempt to "WOW" the audience with their 'state of the art' special effects, ILM have pulled a fast one as well, no doubt in an effort to save time and money, hoping no-one would notice in the process.