Expected:

Enable use_uuid_for_certificates
    Create a host
    Host has a UUID now
    Set host to Build, pull the host's template, watch the certname UUID value be added to the Puppet Autosign file.
    ... realize that uuid certificates aren't right for your organization ...
    Disable use_uuid_for_certificates
    Set host to Build, pull the host's template, watch the certname hostname value be added to the autosign file.

Actual:

Set host to Build, pull the host's template, watch the certname UUID value be added to the Puppet Autosign file.
    Watch as your Puppet run fails to get a certificate because the client has submitted a certificate request using its hostname now.

https://github.com/theforeman/foreman/pull/925