Buttons on the Lock screen don't work consistently

[Justin Mayhew]

When I click the system menu in the top right corner of Unity and then click "Lock", the buttons don't always work. I can type my password and hit enter, which works as expected and unlocks the screen. However, the majority of the time the buttons "Switch user..." and "Unlock" don't work.

If I invoke the lock screen with the keyboard shortcut Ctrl-Alt-L, the buttons always work.

The buttons seem to work about one third of the time when the lock screen is invoked via the system menu.

Ubuntu 13.04 with Unity
gnome-screensaver 3.6.1-0ubuntu3