If you update x11-themes/gnome-icon-theme from version 2.12.1 to 2.14.2 the most icons in evolution won't be available anymore. I have experienced it with evolution-2.6.2-r1 but maybe other versions of evolution or even other gtk-apps are concerned. I don't know whether it is a bug in x11-themes/gnome-icon-theme-2.14.2 or if evolution is only dependent on <=x11-themes/gnome-icon-theme-2.12.1. Regards Sebastian Noack
*** This bug has been marked as a duplicate of 133241 ***