For some reason that eludes me, sharing of the clipboard between the KVM host and the guest (sometimes referred to as clipboard integration) is on by default with QEMU/KVM and SPICE graphics.

To disable such clipboard sharing:

  1. Edit the guest definition XML; virsh edit $GUEST and locate domain/devices/graphics, or through virt-manager’s View > Details > Display Spice > XML
  2. Add or update an element <clipboard copypaste="no"/> under the <graphics> node
  3. Save/apply the change
  4. Fully shut down the VM (if running)

If starting the VM from the command line, another option is to try adding -spice disable-copy-paste to the qemu-system-* command line. (See here.)

Clipboard sharing between the host and the guest will be disabled the next time the VM is powered on.