Comment 6 for bug 573477

Found the line it was talking about in /var/lib/dpkg/info/mdadm.postinst

---------------------------------------SNIP---------------------------------------
    if [ ! -f /proc/mdstat ] && [ -x $(command -v modprobe 2>/dev/null) ]; then
      modprobe -k md >/dev/null 2>&1 || :
    fi
    if [ ! -f /proc/mdstat ]; then
      echo 'W: mdadm: failed to load MD subsystem.' >&2
    fi

    if [ ! -e /dev/md15 ] \
      && [ ! -e /dev/.static/dev/md15 ] \
      && [ ! -e /dev/.devfsd ]; then

        echo -n 'Generating array device nodes... ' >&2
        cd /dev
        if /dev/MAKEDEV md >&2 >/dev/null; then
          echo 'done.' >&2
        else
          echo 'failed.' >&2
        fi
    fi
---------------------------------------SNIP---------------------------------------

I haven't looked further into what that script really should be doing there however.