For any poor saps that encounter this in the future in a similar situation, replacing the graphics driver with 'virtio' in the KVM/qemu config fixes this:
Instead of the default 'cirrus' or whatever. Found this in my age-old notes from the last time I encountered this problem a year ago. I'm not sure whether this triggered a cache clear or whether the bit depth is different or what...
For any poor saps that encounter this in the future in a similar situation, replacing the graphics driver with 'virtio' in the KVM/qemu config fixes this:
<video>
<model type='virtio' vram='16384' heads='1'/>
<address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
</video>
Instead of the default 'cirrus' or whatever. Found this in my age-old notes from the last time I encountered this problem a year ago. I'm not sure whether this triggered a cache clear or whether the bit depth is different or what...