ppc64 + virtio-scsi: only first scsi disk shows up in the guest

When adding two virtio-scsi targets to a single guest, only the first
disk is seen inside the guest.  For some unknown reason the guest
doesn't enumerate the second disk.

For full qemu-system-ppc64 command line and 'dmesg' output, see:

http://lists.nongnu.org/archive/html/qemu-devel/2012-06/msg02430.html

I have also tried this with Linus's git tree (3.5.0-rc2+ at time of writing),
same thing.

In both cases I'm using qemu from git.