Visual diffs in VisualEditor are early in their lifecycle and evolving over time. I've been considering this feature as being in beta, as it's going to change a lot more. We don't indicate that to users anywhere in the interface, though. Should we indicate this to users somehow, so they know they can expect imperfections, and changes over time?
I think something fairly subtle would do fine. Quick and dirty mockup to illustrate the kind of thing I'm thinking of: