Same problem here: after I upgraded gnome-panel from 2.24 to 2.26, the shutdown option disappeared from the menu. However, when you hit Ctrl-Alt-Del, the shutdown dialog appears and the buttons on it work as they should.
-- Dmitry Borodaenko -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org