Lock screen background is all green

I am aware that in Mate 1.16, in Ubuntu 16.04 you can't change the lock screen background. Usually I would just change /usr/share/backgrounds/ubuntu-mate-common/Ubuntu-Mate-Cold.jpg to whatever i like, but now it's not working, and the lock screen is just showing green. The config file at /etc/lightdm/lightdm-gtk-greeter.conf.d/99_ubuntu-mate.conf has no effect on the lock screen.

Can someone point me in the right direction of the config file used in 1.16? Or has anyone had the same green background?

Currently the lock screen is all green: