Comment 12 for bug 854261

I guess I can trace out the problem now:

1. When I change the selected user in lightdm-gtk-greeter user list, function set_displayed_user() is called.

2. lightdm-gtk-greeter's function set_displayed_user(), in turn, calls start_authentication(), which then calls lightdm function lightdm_greeter_authenticate() (or lightdm_greeter_authenticate_as_guest(), if guest login is selected).

3. When autologin timeout expires, greeter calls lightdm_greeter_authenticate_autologin(), which, in turn, calls the same suitable lightdm_greeter_authenticate{,_as_guest}() function as before.

In the end, lightdm_greeter_authenticate{,_as_guest}() is called twice for the same user, and maybe the second call is ignored by lightdm. If this is right, some possible solutions are:

A. In lightdm-gtk-greeter's function set_displayed_user(), check first if selected user matches configured autologin one, and don't call start_authentication() immediately if they match, but only when login button is clicked.

B. In lightdm-gtk-greeters's function start_authentication(), check first if given username matches configured autologin one, and don't call lightdm_greeter_authenticate{,_as_guest}() if they match.

C. In lightdm's function lightdm_greeter_authenticate{,_as_guest}(), allow somehow that a second call for the same user overrides the first call, specially if second call is of autologin kind, and first one is of manual kind.