it seems as if as of sharutils > 4.7, upstream no longer uses /REL-${PV}/ in their paths. Removing /REL-${PV}/ produces proper fallback fetching.
Created attachment 222449 [details, diff] remove /REL-${PV} from SRC_URI
done, thanks http://sources.gentoo.org/app-arch/sharutils/sharutils-4.9.ebuild?r1=1.1&r2=1.2