get "in reply to" with nntplib

[Hanman]

Hello,
I am coding a small newsarchiv and have a question: When trying to read
out the "in reply to" data with xhdr i always get a "(none)" as return.

Example:

s = nntplib.NNTP('freetext.usenetserver.com')
resp, count, first, last, name = s.group('comp.lang.python')
resp, subs = s.xhdr('In-Reply-To', first + '-' + last)
for id, sub in subs[-20:]:
print id, sub

529515 (none)
529516 (none)
529517 (none)
529518 (none)
529519 (none)
529520 (none)
[.....]

What do I wrong?

Many greetings
Hanno