Host Operating System parameter updated by puppet run with update_environment_from_facts = false

Greetings,

the Foreman Host parameter "operating system" is updated by facts from
puppet run even "update_environment_from_facts" is set to false!

Puppet Version 3.7.1
Foreman 1.6.1
Proxy 1.6.2
Installer 1.6.2

Did we miss another setting parameter?

R/Daniel