Currently, xfce4-session uses custom icons for shutdown, reboot and logout. It would be nice if it would use icon-naming-spec compliant icon-names for that.
Created attachment 1604 replaces xfsm-reboot and friends with system-reboot and friends. NOTE: system-shutdown and system-reboot are not part of the icon-naming-spec yet, but they are additions which are commonly accepted. (A discussion is going on @ xdg to add it to the official spec)
*** Bug 3727 has been marked as a duplicate of this bug. ***
Fixed, not replaced the icons. But used the existing icons as a fallback.