Unity8 allows modal dialogs to be minimized, leaving the parent window unoccluded but unresponsive

Can you elaborate further? It seems to me that the settings dialog opens as a new page within the terminal window, rather than as separate windows.

Oh it's a new terminal app "from overlay PPA".

I would hazard a guess the correct title of this bug should be:
"Unity8 allows model dialogs to be minimized, leave the parent window unoccluded but unresponsive."

:D yep, so terminal is installed from here https://launchpad.net/~ci-train-ppa-service/+archive/ubuntu/stable-phone-overlay/?field.series_filter=zesty

so this is pretty easy to repoduce, just start the terminal, click on the cogwheel to open the preference window, minimize the preference window, forget about it, now click again on the cogwheel to bring back the preferences window, nothing happnes.. just the content of the main window gets unfocused (not the title bar), so it's not even super obvious what's going on, not try to type some stuff in terminal.. you can't.. it's pretty confusing for me. i've expected that the preferences window sould just unminimize/restore when pressing the cogwheel :D