I can confirm this bug in Knews (both, in KDE3 and KDE4 versions). This is
a clear violation of RFC2822, which says:

http://www.ietf.org/rfc/rfc2822.txt
# [...]
# 3.5 Overall message syntax
#
# A message consists of header fields, optionally followed by a message
# body.  Lines in a message MUST be a maximum of 998 characters
# excluding the CRLF, [...]

This should be easy to fix, as all it takes is to remove the last 1-2
references to stay below the maximum line length.
A simple testcase is Msg-ID: <gsamsd.1ao.1@ID-4636.user.dfncis.de>;
trying to respond to this message will trigger a "441 437" error by
the posting host (presumed to be RFC-compliant).

I can also confirm this bug.
Pan is working fine in the same conditions, as it is splitting the "References:" header in several lines:
References: <49b02cb1$0$21742$7a628cd7@news.club-internet.fr>
        <gs3u2j$dog$1@writer.imaginet.fr> <49e5ea1a$0$2849$ba620e4c@news.skynet.be>
        <gs4ps4$lnt$1@writer.imaginet.fr> <49e6107c$0$2862$ba620e4c@news.skynet.be>
        <gs6hbf$an4$1@writer.imaginet.fr> <49e704d0$0$2858$ba620e4c@news.skynet.be>
        <3a588689-6712-4a99-b2db-161844d2f006@z7g2000vbh.googlegroups.com>
        <gsao7h$2bfu$3@talisker.lacave.net>
        <49e8f4da$0$2854$ba620e4c@news.skynet.be>
        <gsd9s9$s7e$2@talisker.lacave.net>
        <49eaef9e$0$2853$ba620e4c@news.skynet.be>
        <gsf3lq$1rel$2@talisker.lacave.net>
        <49eb1663$0$17755$ba4acef3@news.orange.fr>
        <gsh8ob$1e0$2@writer.imaginet.fr> <49ecd793$0$2851$ba620e4c@news.skynet.be>
        <gsjn27$o0j$1@writer.imaginet.fr> <gsl4l6$l85$7@talisker.lacave.net>
        <49ee23b5$0$17107$ba4acef3@news.orange.fr>
        <gsldbr$2063$5@talisker.lacave.net>
        <49eeb69e$0$17076$ba4acef3@news.orange.fr>
        <49ef70cb$0$4174$426a74cc@news.free.fr>
        <49ef7db6$0$12625$ba4acef3@news.orange.fr>

In the same conditions, knode generates a single line:
References: <49b02cb1$0$21742$7a628cd7@news.club-internet.fr> <49e6107c$0$2862$ba620e4c@news.skynet.be> <gs6hbf$an4$1@writer.imaginet.fr> <49e704d0$0$2858$ba620e4c@news.skynet.be> <3a588689-6712-4a99-b2db-161844d2f006@z7g2000vbh.googlegroups.com> <gsao7h$2bfu$3@talisker.lacave.net> <49e8f4da$0$2854$ba620e4c@news.skynet.be> <gsd9s9$s7e$2@talisker.lacave.net> <49eaef9e$0$2853$ba620e4c@news.skynet.be> <gsf3lq$1rel$2@talisker.lacave.net> <49eb1663$0$17755$ba4acef3@news.orange.fr> <gsh8ob$1e0$2@writer.imaginet.fr> <49ecd793$0$2851$ba620e4c@news.skynet.be> <gsjn27$o0j$1@writer.imaginet.fr> <gsl4l6$l85$7@talisker.lacave.net> <49ee23b5$0$17107$ba4acef3@news.orange.fr> <gsldbr$2063$5@talisker.lacave.net> <49eeb69e$0$17076$ba4acef3@news.orange.fr> <49ef70cb$0$4174$426a74cc@news.free.fr> <49ef7db6$0$12625$ba4acef3@news.orange.fr>

and the result is a 411 error from my news server: "Line too long".

*** Bug 221644 has been marked as a duplicate of this bug. ***

This bug has only been reported for versions before 4.14, which have been unsupported for at least two years now. Can anyone tell if this bug still present?

If noone confirms this bug for a Framework-based version of kdepim (version 5.0 or later, as part of KDE Applications 15.08 or later), it gets closed in about three months.

Just as announced in my last comment, I close this bug. If you encounter it again in a recent version (at least 5.0 aka 15.08), please open a new one unless it already exists. Thank you for all your input.