As sys-apps/shadow is a GNU-specific package (the same commands and facilities are provided by the base system in a BSD userland), the two packages in summary must depend on it just for userland_GNU . The attached patches fixes this. Thanks, Diego
Created attachment 66379 [details, diff] gnome-system-tools-ebuild.patch
Created attachment 66380 [details, diff] system-tools-backend-ebuild.patch
No problem. Feel free to commit your fixes.
Thanks Leonardo, both committed.