While trying to perform an 'emerge -e system' on a fresh gentoo installation, I noticed that sys-apps/shadow-4.1.4.3 can't be fetched due to an invalid SRC_URI. Reproducible: Always Modifying the SRC_URI line in the ebuild to SRC_URI="http://pkg-shadow.alioth.debian.org/releases/shadow-${PV}.tar.bz2" solved the problem for me.
if your GENTOO_MIRRORS is empty, then your system config is broken http://sources.gentoo.org/sys-apps/shadow/shadow-4.1.4.2-r6.ebuild?r1=1.7&r2=1.8 http://sources.gentoo.org/sys-apps/shadow/shadow-4.1.4.3.ebuild?r1=1.7&r2=1.8
