So I review a suggested edit on UX.SE, skim down to the edited bits, and this greets me:
Yes, the highlighted bits are completely identical. But if you hover over the text, you'll find the text on the right gets an underline. What happened here is the user added links to the highlighted words. I see this fairly often.
Would it be possible to make it more clear when an edit added links to body text? It seems like showing the link color (blue in this case) over the highlight color might be enough, but I'm not sure that works as well across all sites (for instance, on Programmers links are red, red links on a green highlight would be bad).