I have a theory on what is causing this...
Disney has a very intrusive process for restoring their animated films. They rotoscope the character off of the backgrounds frame by frame. Then they combine all the backgrounds into a single image and clean that up digitally. The characters are cleaned up and recolored frame by frame. Then the characters are recomposited over the still frame of the background. This eliminates all gate weave in the backgrounds and allows them to totally rework every aspect of the scene.
With hand inking, you have a sharp clean line to use for cutting the character out and removing it from the background. But xerox lines are feathery and vague at times, just like the pencil lines of the animator. When they cut the characters out of the frame, they probably lose most of the edge of the xerox in the process. If they comped it back in like that, it would look like there was no line around the outside perimeter of the character. So they probably do a selection of a tiny sliver of the outer edges and darken it to beef up what's left of the line.
However, when they do this, I bet the result looks like a funky matte line. The beefed up edges are darker and more opaque than the interior xerox lines. To make it match, the select ALL of the black lines and beef them all up equally. This gives a nice, neat thick black line with no vagueness or inconsistency, but it also totally destroys the line weight and shapes of the lines.
The average person may think that "a line is a line". But to an animator, a line is all he has to create the illusion of volume and weight. Animators vary line thickness to define shapes and carefully point the ends of their lines to create the illusion of the volume turning. When you monkey around with this, you are totally compromising the thing that set Disney apart from its competitors- The quality of the finish- really nice cleanup that preserved the animator's volumes.
The technicians massacring this stuff probably think, "no big deal- a line is a line". But I can guarantee you that the animators I know are up in arms about this. They see it as the absolute worst thing you can do to a film. Edit it, make it B&W instead of color, change the soundtrack, recolor it... But don't mess up the lines.