Default XKBLAYOUT is not used, so new users only have "en" layout

I installed Ubuntu 12.04 in Greek.
The following were correctly put in my /etc/default/keyboard:
XKBMODEL="pc105"
XKBLAYOUT="us,gr"
XKBVARIANT=","
XKBOPTIONS="grp:alt_shift_toggle,grp_led:scroll"

The user that did the installation correctly has the option to switch between "English (us)/Greek (gr)" in lightdm, and gets the keyboard switching applet in the panel indicator.
His /var/lib/AccountsService/users/alkisg contains:
XKeyboardLayouts=us;gr;

I create a new user, either with the UI, or with adduser.
Before she logs in, while still in lightdm, she doesn't have the option to switch between "English (us)/Greek (gr)".
After she logs in, she doesn't get the keyboard layout applet.
Her /var/lib/AccountsService/users/newuser contains:
XKeyboardLayouts=

So I guess the problem is that either accounts-service should return the system-wide XKBLAYOUT for new users,
or lightdm should read the system-wide defaults when accounts-service returns "unset".

Here are the results of `setxkbmap -print` for the user that did the installation, where everything is fine:
xkb_keymap {
 xkb_keycodes { include "evdev+aliases(qwerty)" };
 xkb_types { include "complete" };
 xkb_compat { include "complete+ledscroll(group_lock)" };
 xkb_symbols { include "pc+us+gr:2+inet(evdev)+group(alt_shift_toggle)" };
 xkb_geometry { include "pc(pc105)" };
};

And here they are for the new user, which doesn't have the ability to switch the keyboard layout:
xkb_keymap {
 xkb_keycodes { include "evdev+aliases(qwerty)" };
 xkb_types { include "complete" };
 xkb_compat { include "complete" };
 xkb_symbols { include "pc+us+inet(evdev)" };
 xkb_geometry { include "pc(pc105)" };
};