Comment 6 for bug 1713549

And note with pristine-tar the way it is in the branches to land today, that will happen earlier (failing with a dirty tree), because gbp is quite unhappy. We could loosen that, after landing those commits, with the knowledge that gbp will fail (which probably means we need to handle that failure more cleanly) to extract the tarballs.

I think the discussion here is exactly the question :) are we building working-tree or HEAD?

If the former, and there are changes to the upstream, there's nothing we can do, afaict. You need to convert it to a quilt patch in order for dpkg-buildpackage to succeed (that was the message from the original bug report). Changes to debian/ should still work (I believe this is actually the case before pristine-tar lands).