Thank you for your bug report, does it happen if you use the gtk greeter? lightdm itself doesn't decide on resolution, it's either and xorg issue or a problem with gnome-settings-daemon in the unity-greeter
Thank you for your bug report, does it happen if you use the gtk greeter? lightdm itself doesn't decide on resolution, it's either and xorg issue or a problem with gnome-settings- daemon in the unity-greeter