Comment 8 for bug 291712

This was originally reported in gnome-power-manager, but I am sure that bug got fixed. The later comments are due to indicator-session. If you suspend via the indicator applet menu, gnome-power-manager is not being used, since indicator-session calls devicekit to do the suspend.

If you use a hardware button, gnome-power-manager will take care of suspending, and also locks the screen.