A Debian user submitted the bug mentioned in the subject to the Debian Bug
Tracking System. I think I have verified the existence of the bug, but I am
not entirely convinced that I've worked out the logic "time zone sorting"
yet. Anyway, the bug is reproduced below, and available at
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=163045 :

Package: pan
Version: 0.13.0-4
Severity: minor


In the header pane, threads are sorted by the date/time stamp of the
first undeleted article.  If threading is not turned on, then all
articles are threaded this way.

Pan appears to assume that the time found in each article's "Date:"
header is in GMT; the timestamp that's displayed for the article
in the rightmost column of the header pane is corrected to the user's
timezone.

However, Pan does not appear to respond correctly if the time in
the article's "Date:" header is instead in a specific timezone,
with a trailing GMT offset given.  Instead, it takes the time only,
ignoring the offset, assumes that time to be a GMT time, and wrongly
corrects that time to the user's local timezone.

For example, if the user is on the east coast of the US (currently
GMT - 4), and Pan encounters an article posted by someone on the
US west coast (GMT - 7), with a Date header such as:

Date: Tue, 1 Oct 2002 19:59:47 -0700

Pan will not sort this in the header pane as if it was posted at
22:59:47 ET; instead, Pan will think that this was posted at
19:59:47 GMT, and will subtract four more hours off, sorting it as
if it were posted at 15:59:47 ET.

HTH.

-c

-- System Information
Debian Release: testing/unstable
Architecture: i386
Kernel: Linux stax 2.2.19pre17 #1 Tue Mar 13 22:37:59 EST 2001 i686
Locale: LANG=C, LC_CTYPE=

Versions of packages pan depends on:
ii  libatk1.0-0                   1.0.3-2    The ATK accessibility library
ii  libc6                         2.2.5-14.3 GNU C Library: Shared libraries an
ii  libglib2.0-0                  2.0.6-1    The GLib library of C routines
ii  libgtk2.0-0png3               2.0.6-3    Dummy package for libgtk2.0-0
ii  libpango1.0-0                 1.0.4-2    Layout and rendering of internatio
ii  libpango1.0-common            1.0.4-2    Modules and configuration files fo
ii  libxml2                       2.4.24-1   GNOME XML library
ii  zlib1g                        1:1.1.4-4  compression library - runtime