virtManager/config.py has this little stanza in `get_default_cpu_setting`, the method for returning the 'default' CPU model:
if for_cpu and ret == CPU.SPECIAL_MODE_HOST_MODEL:
# host-model has known issues, so use our 'copy cpu'
# behavior until host-model does what we need
ret = CPU.SPECIAL_MODE_HOST_COPY
I believe the 'known issues' referred to there are those documented in https://bugzilla.redhat.com/show_bug.cgi?id=870071 , which is closed from libvirt 3.2.0 onwards.
Perhaps this workaround should now be removed, or made conditional on libvirt < 3.2.0, at this point?
Note: I'll be opening a similar issue on Boxes, which acts similarly.
*** This bug has been marked as a duplicate of bug 1055002 ***