Ping of Hostname is always extended by domain?

Hi,

i set a FQDN domainname as hostname on our UTM appliance: utm.example.com (example.com = domain of our Website).

If i ping any hostname (not FQDN) under Support -> Tools -> Ping i get e response from our external server because UTM always extends the hostname with example.com. e.g.: unifiy becomes to unify.example.com and gets a external ping response from our external webserver. 

Why is the UTM extending all hostnames with the domain part of its own FQDN? How can i get rid of this behavior?

Thanks
Patrick