[libvirt-users] /etc/machine-id

I was under the impression that the value of /etc/machine-id was unqiue for every OS installation on a system. This seems to be the case on real hardware. That is, if I install Fedora 19, Fedora 20, and Fedora-rawhide on a system, they will each have a different value for /etc/machine-id. This does not seem to be the case for qemy-kvm-libvirt virtual systems. SOmetimes they are different but I just noticed that a virtual system with both Fedora 20 and Fedora rawhide installed (btrfs partitioning), the two installations have the same value in /etc/machine-id. The two installs have different ext4 partitions for /boot, different subvols for the respective rootfs and the same/shared subvol for /home. Comment? Bug? Gene