I'm sorry to say that I've been playing with this for only a week -- not long enough to say anything at all about xfs. But the solution, of editing the cp command, seems a sure-fix. I've done it several times now. It always fails at about the same place without making the change, and it always works, with the change.
I've got a spare PC to play with and I'm going to be working with it over the next several weeks. I'll keep you posted.
Other forums that I frequent, have nothing but good things to say about xfs. The only drawback is that it requires a patched kernel.