Ubuntu 12.04 has an earlier implementation of multiarch where it uses the --foreign-architecture options that you see in /etc/dpkg/dpkg.cfg.d/multiarch. Newer versions of ubuntu have the latest multiarch implementation where dpkg --add-architecture is supported.
This is not a bug. I don't know what you expect. In any case, the new multiarch implementation won't be deployed to LTS 12.04 at this point.
Ubuntu 12.04 has an earlier implementation of multiarch where it uses the --foreign- architecture options that you see in /etc/dpkg/ dpkg.cfg. d/multiarch. Newer versions of ubuntu have the latest multiarch implementation where dpkg --add-architecture is supported.
This is not a bug. I don't know what you expect. In any case, the new multiarch implementation won't be deployed to LTS 12.04 at this point.