you know, I've just checked both versions(nelly's and Tempest) myself using a remarkable song-edition software, and I reached at the following conclusion: Too much coincidence.
OK, there are variations from one song to another, but still the "melodic structure" is quite similar, as if one were a sang version of the other.
I guess if we all, human beings, were a bit more honest inside -not to show off- these kinds of situations would be prevented; just because of the fact that we would be trying to to be kind, to do the right thing concerning other people (not to rip a song composed by a perhaps-unknown author,for instance, in this particular case); ethics.
don't know, that's what I think. We'd all feel better.