Dear Maintainer,

When a QEMU guest without spice-vdagent runs on a VM with virtio-vga,
the guest doesn't receive mouse input. (Tested on Debian Sid as the
guest.) This behavior confuses remote-viewer connected to it through
SPICE; when the cursor enters a focused remote-viewer window (i.e.
the window is the top window), the cursor disappears, and it doesn't
reappear even after mouse movement.

To make the cursor usable again, pressing Shift+F12 does *not* suffice.
(However, in some cases, it may be necessary to press Shift+F12 before
carrying out the following step.) To ungrab the cursor, one needs to
unfocus the remote-viewer window. (This can usually be done by pressing
the Windows key.)

However, this issue does not manifest when the guest runs spice-vdagent;
in that case, the cursor can be moved and can exit the window.

Nor does this issue happen when remote-viewer is connected to a VM with
QXL graphics; the host cursor disappears when it enters the remote-viewer
window, but it can exit the window. Interestingly, VMs with QXL can
receive mouse input even without running spice-vdagent, unlike VMs
with virtio-vga.

Host system information generated by reportbug is attached. I experience
this bug on KDE Plasma on Wayland.

Best Regards,
Samuel Plavec