Package: virt-manager Version: 1:1.4.2-1 Followup-For: Bug #857731 virt-manager recommends libvirt-daemon-system; however without it it is not possible to create a new machine. Installing libvirt-daemon-system fixes the problems, at least for QEMU (but most possibly for anything else as well).
It should be a stronger dependency; possibly even depends, since this is one of the main functionality of virt-manager.