[ovirt-users] Linux guests vs. Spice/QXL?

Hi all, I'm running some tests on OVirt (3.6.5.3) on CentOS 7 and almost everything works quite well so far. CentOS 6.x, Windows 7 and 2008R2 work fine with Spice/QXL, so my setup seems to be ok. Other Linux systems don't work: Debian 8, Fedora 23/24, CentOS 7.x, Kubuntu 16.04... CentOS 7.x even kills his X server every time the user logs out. X-) They all have in common that they show a fixed display resolution of 1024x768 pixels. This can not be changed manually and of course automatic display resizing doesn't work either. All machines have spice-vdagent and ovirt-guest-agent installed and running. Is this a local problem or is this known/expected behaviour? Is there anything I can do to improve this? thank you, Uwe