Weird behavior of 'git log --before' or 'git log --date-order': Commits from 2011 are treated to be before 1980

[Thomas Bock <bockthom@cs.uni-saarland.de>]

Dear git development team,

I've spotted a weird behavior of git in a specific repository, which I 
cannot explain, maybe there is a bug in git.

Repository in which the problem occurs:

git@github.com:LibreOffice/core.git

Problem:

When ordering the commits in this repository by time via "git log", 
there are several tens of commits which appear to be before 1980 
although their author date and commit date are in 2009 or 2010 or 2011.

Example to reproduce:

git clone git@github.com:LibreOffice/core.git libreoffice
cd libreoffice
git log --no-merges --before="1980-01-01T00:00:00+0000" 
--format=%H,%ct,%ci,%ad

All the resulting commits have an author date and commit date in 2009 or 
2010 or 2011, though.

This also appears when you order the commits by date:

git log --no-merges --date-order --format=%H,%ct,%ci,%ad

If you search for commit d3b03514dde317473db0d247f21405b5db6a727e in the 
resulting output, you can see that this commit is placed earlier in the 
list than the commits from 2008 although its author date and commit date 
are from 2011. And there are many more commits of this sort between 2009 
and 2011 which are placed out of order, interpreted to be earlier than 
every other commit.

I already searched for broken timestamps in these commits and printed 
the timestamp in various different formats, but I could not spot 
anything dubious there. So, why does git log think that these commits 
have an earlier timestamp than they actually have?

Thanks for your efforts!

[System Info]
git version:
git version 2.30.2 (but I have also tried it with git version 2.40.0 
with no difference)
cpu: x86_64
sizeof-long: 8
sizeof-size_t: 8
shell-path: /bin/sh
uname: Linux 5.10.0-21-amd64 #1 SMP Debian 5.10.162-1 (2023-01-21) x86_64
compiler info: gnuc: 10.2
libc info: glibc: 2.31
$SHELL (typically, interactive shell): /bin/bash

Best,
Thomas