@RLane Yes that is how it works.
I did create a hack to make a pseudo persistent groups if you want to give it a try. Understand this is unsupported by the FOG Project. So use it at your own risk.
https://forums.fogproject.org/topic/6902/fog-1-3-persistent-groups/12
But what happens here is that the sql script creates a trigger when a device is connected to a group. That trigger will look in the list of hosts for a host name that is the same as the group name. If it finds a host with the same name as the group name, it copies the fields for that host into the host that was just inserted into the group. It sounds complicated but its not. Just install the trigger and then create a group and host name that matches exactly. Then just add the computers to the group and the group setting should be persistent.