I encountered an issue when updating the intel64-silvermont gnome stage3 image.
net-mail/bogofilter failed to build. I can attach the build log. It looked related to sys-libs/db. So I entered the metro chroot, tried emerging bogofilter, and it still failed. I re-emerged sys-libs/db, and then bogofilter built fine.
I think we should look into triggering sys-libs/db to rebuild (db-18.1.32 is the specific version) when glibc is updated.