gnus and gnupg gives me sometimes bad signature result

[Rud1ger Sch1erz]

Hi,

for some news articles emacs/gnus gives me a bad signutare, e.g. with

  Message-ID: <CfV-1-de.etc.selbsthilfe.angst|gehoer-24.12.2010@dana.de>

[[PGP Signed Part:Bad signature from CAAD11864B666561 David Seppi 
<david.seppi@dana.de>]]

Thunderbird otoh says, the signature is good and the signature seems
really to be good, as the poster and other users seconded. 

This problem occurs with some articles only, others are ok.

Any idea? 

Cheers,
Rudiger

GNU Emacs 23.1.1 (i486-pc-linux-gnu, GTK+ Version 2.20.0) of 2010-03-29
on rothera, modified by Debian

Gnus v5.13

gpg (GnuPG) 1.4.10