Ok. When you create fresh template, named for instance fedora-26, now you have to create disposable template named for instance fedora-26-dvm:
[user@dom0 ~]$ qvm-create --template fedora-26 --label red fedora-26-dvm
[user@dom0 ~]$ qvm-prefs fedora-26-dvm template_for_dispvms True
[user@dom0 ~]$ qvm-features fedora-26-dvm appmenus-dispvm 1