[Nursie]

Your patch would be meaningless without the GPL code underneath, so is a derivative work and would therefore likely fall under the GPL.

[Dylan16807]

Requiring another work for meaning, without actually including any of that work, is not enough to make copyright kick in as far as I know.

[Nursie]

Then any source patch would fall outside of licensing.

It's clearly a derivative work, as described.

[Dylan16807]

Some source patches include significant elements of what they apply to.

Some don't.

[geofft]

I think that argument would also imply that you don't need a copyright license to write a sequel to a book (assuming you don't quote the book, but the sequel includes characters / plots from the original book), and I think it's the case that a sequel is a derivative work. So by contradiction, it doesn't matter if the patch to the source includes a nontrivial portion of the source; it's still based on the source either way.

[Nursie]

That's not the issue at all, it's still a derivative work, regardless of whether it contains much of the original.