socket.getfqdn() returns no domain, but socket.gethostname() does?

I do not understand this:

Python 2.7.3 (default, Apr 14 2012, 08:58:41) [GCC] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import socket
>>> socket.getfqdn()
'SR-MW001'
>>> socket.gethostname()
'sr-mw001.foo-domain.de'

What is wrong here?

According to the docs of socket.getfqdn() the "a fully qualified domain name" should get returned.

from socket.getfqdn() returns no domain, but socket.gethostname() does?