I did a GP Check and put it into diff located here:
http://dl.dropboxusercontent.com/u/72762463/diffnew.html
A bit of context. When checking this, I didn't change the first paragraph at all.
When I pressed diff with an edit cost of three and timeout of one, it gave me this, substituting abstract sentences in brackets for their actual visual representations:
<First paragraph of the original/new, in black text>
<Remainder of the original, in red crossed-out text>
<Remainder of the new, in green text>
Having done a GP check before, I know this isn't what's supposed to happen. I also tested some simpler examples (typing asdf a bunch in the original and changing some in the new) and confirmed that the program isn't completely defunct.
I'm not sure why this happened with my check, and wondered if anyone might know. If I haven't provided enough information here to answer the question, I'll happily send a PM to anyone willing to look at it and tell me what I'm doing incorrectly.