On current Fedora Rawhide, if I run a virtual machine in virt-manager, I cannot see the VM's display on the 'graphical console' tab as usual. The area where it should appear is just blank grey. virt-viewer behaves the same way, but if there's a shared component that handles this I don't know what it is, so filing against virt-manager for now. This happens whether the VM is using VNC or Spice. If I run virt-viewer at a console, I see what seems like a possibly-significant error: (virt-viewer:5542): Gtk-WARNING **: Allocating size to VncDisplay 0x562471606270 without calling gtk_widget_get_preferred_width/height(). How does the code know the size to allocate? When using Spice there's a similar message only referencing 'SpiceDisplay' not 'VncDisplay'. I haven't run a VM on this box for a while so I don't know for sure, but this *may* have started with GTK+ 3.19.9, which landed recently.
This bug appears to have been reported against 'rawhide' during the Fedora 24 development cycle. Changing version to '24'. More information and reason for this action is here: https://fedoraproject.org/wiki/Fedora_Program_Management/HouseKeeping/Fedora24#Rawhide_Rebase
*** This bug has been marked as a duplicate of bug 1311612 ***