Host: 
- Debian Linux with kernel 3.11-2-amd64
- QEMU emulator version 1.7.0 (Debian 1.7.0+dfsg-2)
- Spice server 0.12.4
- libvirt Virtual Machine Manager 0.9.5

Guest:
- Ubuntu Saucy with kernel 3.11.0-20-generic

Reproduce:
- Start qemu with option -global qxl-vga.revision=4, which allows drm to load
the 
  qxl driver
  Other parameters related to graphics:
  + -device
qxl-vga,id=video0,ram_size=67108864,vram_size=67108864,bus=pci.0,addr=0x2
  + -spice port=5900,addr=127.0.0.1,disable-ticketing,seamless-migration=on
  + -chardev spicevmc,id=charchannel0,name=vdagent
  + -device
virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=com.redhat.spice.0
- Check with dmesg, that QXL DRM has been correctly initialised
- Send Ctrl-Alt-Fn (n = 1, 2, ...) to VM guest

Bug:
Virtual machine manager will switch to console but freezes with strange
display. Guest cannot be contacted any more. Switching back to vc is not
possible. ssh connections will hang. No netconsole output. The guest must be
restarted using forced shutdown.

The problem occurs also for qemu 2.0. It does not occur, if only userspace
driver is used (omit option -global qxl-vga.revision=4). In this case lspci
reports:
00:02.0 VGA compatible controller: Red Hat, Inc. Device 0100 (rev 03)
and dmesg reports:
[drm] Initialized drm 1.1.0 20060810
[drm:qxl_pci_probe] *ERROR* qxl too old, doesn't support
client_monitors_config, use xf86-video.

I can provide further information, but need some guidance, what you prefer in
order to locate the root cause of the problem.