I already explained this.
1. Stop adding users to a new group when they register. Just leave it alone.
2. Whatever role you created for users in the helpdesk (as opposed to staff), add the Registered Members group to that role, it should be the first on the list, as per http://www.simpledesk.net/community/index.php?topic=709.0 - last screenshot in the first post, the first group is the registered members group. Any user who just registers will be in that group (even though it will not show it on posts, this is intentional in SMF, but they WILL be in that group)
1. Stop adding users to a new group when they register. Just leave it alone.
2. Whatever role you created for users in the helpdesk (as opposed to staff), add the Registered Members group to that role, it should be the first on the list, as per http://www.simpledesk.net/community/index.php?topic=709.0 - last screenshot in the first post, the first group is the registered members group. Any user who just registers will be in that group (even though it will not show it on posts, this is intentional in SMF, but they WILL be in that group)