bug#45724: 27.1; gnus vs. raw big5 headers vs. the second day

["積丹尼 Dan Jacobson" <jidanni@jidanni.org>]

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Yes the mails we receive have properly mime encoded headers.
But let's say some agency sends an email with ancient illegal raw big5
headers:
$ iconv -f big5 headers.txt
Subject: 內政部部長電子信箱受理通知編號:20210108003         
From: "內政部部長電子信箱" <returnecss@minister.moi.gov.tw>

Well, on the first day, things work fine in gnus.

But on the second day upon reopening gnus, the headers have "degraded":


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The *Summary* buffer has now a garbled line. Howver the *Article* buffer
is still doing fine.

Funny thing is, if we pipe the second article through procmail, and
enter gnus again, the newly created identical third article has an OK
*Summary* line.

Important settings:
  value of $LC_COLLATE: C
  value of $LC_CTYPE: zh_TW.UTF-8
  value of $LC_MESSAGES: C
  value of $LANG: zh_TW.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

(One also notes raw big5 enters the .overview file, but not always.)

My dot files are at https://www.jidanni.org/comp/configuration/

Anyway, sure, gnus can deal with such wacky headers fine on the first
day.

But on the second day, after totally quitting emacs and starting up
again, such headers are no longer dealt with properly, at least in the
*Summary* buffer.

Sure, "Tell the agency to stop sending illegal headers." Well, yes...