The reason is, when host is created normally, we apply inherited attributes thanks to

https://github.com/theforeman/foreman/blob/c03c4a44a8c7891aeb470a2fde3f486199299177/app/models/host/managed.rb#L77-L80

The registration skips this and calls directly assign attributes

https://github.com/theforeman/foreman/blob/develop/app/controllers/api/v2/registration_controller.rb#L110-L119

That should be changed so the inheritance logic works like when the new host is created through the form.

This issue is still present on Foreman 3.5.1.

Steps to reproduce:
- Create a Host Group
- Select 'Puppet Proxy', 'Puppet CA' and 'Environment' from the relevant Pull-Down-Menus on the Host Group
- Create a Global Registration Template associated with the newly created Host Group
- Register a client using the Global Registration template

The client is registered, but Puppet Parameters from the Host Group are not adopted, leading to empty ‘Environment’ ‘Puppet Proxy’ and ‘Puppet CA Proxy’ on the host object and a puppet.conf on the client which looks like this:

[main]

[agent]
pluginsync      = true
report          = true
certname        = my.host.tld

The issue does not occur if the host object already exists and Puppet settings are defined on the host object.

A partial workaround, still leading to a non-functional result, is to define puppet_ca_server and puppet_server as Parameters on the hostgroup. In this case server and ca are written correctly, but environment not. Trying to set the host_puppet_environment parameter manually on the host group, still leads to the same result (variable empty)