FortiGate 500D, v5.2.3,build670 (GA) - Tracking un-registered clients

I've got a pair of 500D in HA.  I see that even when I manually un-register FortiClient, it still tracks the devices and they're counted against the total of available clients.  Is there a method to remove these un-registered clients from the count?

Edit: Looking at diagnose endpoint registration summary, I see a different list than in the GUI.  Why the difference?

The CLI output is correct, but there are hosts listed in the GUI that are not visible in CLI and hosts in CLI that are not visible in GUI.