Just throwing this out there, but I wouldn't put it past George Lucas to have made a quick last minute change to his film shortly after its premiere. He might have thought that the composite was flawed in that one shot, and managed to squeeze out a bit more money from the budget to fix that one shot (other bothersome shots like Mos Eisley would have been too expensive to fix). So in the end we have two different IPs running around: "Premiere 77" and "Post-Premiere 77". That might explain why the IB has the cloudless version.

EDIT: just saw your post about the credits. Again, George just couldn't keep his hands off of it and kept trying to make it better. There were even 3 different sound mixes for it! It seems very likely that he would go back and change a few things to the picture as well.