display channel width/height properties appear incorrect

This may be user error but I need some help. I'm coming from this virt-manager bug: https://github.com/virt-manager/virt-manager/issues/165

Certain resolutions inside a VM are not reflected correctly in the display channel width+height properties. For example with 1360x768 inside the VM, 'width' consistently reports 1408. I confirmed this by adding printf to virt-viewer code too to ensure it's not virt-manager specific. However virt-viewer gets the final resolution from the 'monitors' property, though accessing that on python is busted: #132

For most common resolutions it seems like correct values are reported. See the virt-manager issue above for some more data.

Is width + height expected to be usable in this way? Are we doing something wrong in virt-manager or is this a spice-gtk bug?