Again, when you see the forthcoming re-edit of ANH and ESB that I've done, I hope I've done this awful continuity error some justice.

Yes, I'm teasing the issue to build up interest, but I really did handle this problem. Because Gaffer Tape hit the nail on the head. Vader already knows. And Lucas clearly hasn't watched ESB and studied it in a long time. I'm sure he just thought it would be cool to add this bit of dialogue without thinking about continuity. Why the F doesn't anybody at Lucasfilm ever point this stuff out to him?!?!?!?!?!?