This is 100% reproducible for me, but could be affected by my guest machine config, I guess. My host here is running F19 (my regular desktop). I have a VM into which I've done a normal install of F19 Beta TC3. If I boot the guest to multi-user.target (runlevel 3, console only) and trigger a Reboot from the host (in virt-manager's guest window, click Shut Down then Reboot from the top bar), the system reboots (very swiftly; doesn't look like a clean shutdown, though IMBW). If I boot the guest normally and leave it at GDM, and trigger a Reboot from the host, nothing at all happens. If I boot the guest normally, log in to GNOME, and trigger a Reboot from the host, the guest suspends instead of rebooting. If I then resume the guest and run 'shutdown' from a console, the guest reboots instead of shutting down. Looks like there's some kind of wacky interaction between libvirt and GNOME, here?
Created attachment 745467 [details] XML of the guest
*** This bug has been marked as a duplicate of bug 744077 ***
I've been begging GNOME developers to fix their default handling of ACPI wihtin a guest since at least F16. Meanwhile, we _still_ don't have out-of-the-box guest agent working, which would also let us avoid the need to react to ACPI in the first place.