Here's what I'm doing. First, I use the GUI to create an appvm, called let's say "my-dvm". Then,
[user@dom0 ~]$ qvm-prefs my-dvm template_for_dispvms True
[user@dom0 ~]$ qvm-features my-dvm appmenus-dispvm 1
Then, I see "Disposable: my-dvm" in the launcher, as expected. But the problem is if I start a terminal from the launcher, it launches "my-dvm" and not i.e. "disp1234". That is, when creating a debian-9 based dvm template, its the template that launches, not a dvm.
If I repeat the procedure, but select fedora-29 as the template (instead of debian-9), the it works as expected, launching a vm titled "disp1234" (for example).
Note, I recently upgraded debian-9 template to the testing respository version (because of apt-get security issue).