There are shots in RotJ that apparently gave away the makeup effect of the Emperor. To cover this up, they put a black blob on the right side of his hoods interior. R2, they were there in theaters. Projected film has a much richer black scale that allows the blobs to vanish, like they're suppoed to. The problem is that video doesn't have nearly as good a black scale. Hence the slugs and garbage mattes resurface.