We currently use the application icon for items that are grouped by application and the window icon otherwise. However with the icon property being unused anywhere else in GNOME3, applications have started to not set any window icon at all. Rather than complaining to application authors, switch to using the app icon everywhere, which improves consistency with the rest of GNOME3 anyway. https://bugzilla.gnome.org/show_bug.cgi?id=694850