To add: I also installed mutter from Debian testing (required installation of Xwayland as well), ran it with 'mutter --wayland --nested', and I could run SystemPreferences from it.
Unfortunately, the window doesn't display initially (it's invisible, kind of like the experience I had attempting to merge Sergio's patches). However, this time around, I can click around and eventually something happens and the windows do get painted. Interestingly, app menu (whether floating or global docked menu) and the dock icon are painted correctly. I would not be surprised if fixing the xdg_surface not being configured would fix the problem in Mutter as well. Thoughts?
