Updating today, suddenly a whole bunch of icons are broken; GNOME shell was presenting everything with a generic application diamond as its icon. Bah.
I noticed gnome-icon-theme was one of the packages that bumped. It turns out that package is now only a limited subset of the GNOME icon set and that you have to install gnome-icon-theme-full to get the icons you actually need. Bah², but now everything is back the way it should be.
AfC