cannot timeout suspend GDM from logind

[KeithG]

Previously (12.04 - 15.04), if I edited the /etc/systemd/logind.conf file to auto suspend the GDM login screen it worked. Now, if I edit the 2 lines to cause a suspend if the login screen (GDM) is up and no one logs in for 15 minutes, I get unintended random suspend from an active, logged in user.

The edit I make is to uncomment 2 lines:
...
IdleAction=suspend
IdleActionSec=15min
...

This happens with 15.10 and 16.04 and is repeatable on my 3 machines. 1 is nvidia current, another nvidia legacy and another is i915. All were clean installs (not upgraded)

Release:
Description: Ubuntu 16.04 LTS
Release: 16.04

Version:
systemd:
  Installed: 229-4ubuntu5
  Candidate: 229-4ubuntu5
  Version table:
 *** 229-4ubuntu5 500
        500 http://us.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     229-4ubuntu4 500
        500 http://us.archive.ubuntu.com/ubuntu xenial/main amd64 Packages

What I expect:
If no user is logged in, the GDM screen should suspend. If a user is logged in, it should not suspend

What happens:
after a user logs in, the computer will suspend after 15 min. There is nothing odd in the dmesg log. It just appears as any suspend event. If a user is logged in, it should not suspend unless the user has a timeout and suspend set fort their login.