Follow-up:
Noticed a new minor annoyance: Some times while in convergence, if you shut down Fedora it 'forgets' the window size you started with at boot up. What you get is the smallest window possible, then have to stretch it back to size. Weird.
Current versions:
Parallels 14.0.1 (45154)
Fedora 28, kernel 4.18.7-200
Gnome 3.28.2