How to hide a user in lightdm login menu?

Hello

I try to hide a user login from the lightdm login menu

I have a second user, ftp-user (with a UID of 501) and I want to hide this user in the lightdm login menu.

I found in /etc/lightdm/users.conf this line:
But when I add my user to hide nothing happens.

Another option I found is in /etc/lightdm/lightdm.conf:
which, when enabled, does hide ALL users - but I only want to hide a particual user.

somehow /etc/lightdm/users.conf is ignored (which option seem to allow to do what I want)

Is there anyone with a idea how I can do this

Thanks in advance

System:
openSuSE 13.1 64 bit with XFCE desktop