Comment 6 for bug 854261

I can confirm this with lightdm-gtk-greeter at Xubuntu 15.04.

I have a 2-seat computer and lightdm configured to autologin as a given user (also applies for guest) on both seats. If the user configured for autologin on a given seat is selected in user list when timeout reaches 0, it won't autologin. However, if I change the user selected before timeout reaches 0, autologin works as expected.

Not sure if it also happens for unity-greeter.