I just checked with my co-worker:

<\mjd> rjbs: Have you ever used the "edit this hunk" subfeature of git add -p?
<rjbs> yes, often
<\mjd> Every time I do it, git rejects my edited patch, saying it won't apply cleanly.
<rjbs> huh
<rjbs> I don't think I've ever had that happen

I'll ask around and let you know if I find out anything.