Comment 2 for bug 19631

(In reply to comment #1)
> Other users have confirmed this problem on ubuntu-devel / IRC. Do you know the
> cause?

I think i see it. In the initramfs, the /scripts/local-top/lvm script contains this
line:
    vg=$(echo ${ROOT} | sed -e 's#/dev/mapper/\(.*\)-.*#\1#')
and then runs
    vgchange -ay ${vg}
which throws up the error 'Unable to find volume group...etc'

So, the above sed needs to be something more like:
    sed -e 's#/dev/mapper/\(.*[^-]\)-[-]\?[^-]*#\1#'
which should handle vgvgvg-lvlvl, vg-vg-vg-lv, vgvgvg--lvlvlv, etc.