Thanks for the bug report. I reproduced the problem and installed the
attached patch to fix it.
>From b8375c422ffe0e018cbb4cad187d1e909195d263 Mon Sep 17 00:00:00 2001
From: Paul Eggert
Date: Fri, 15 Jan 2021 02:57:59 -0800
Subject: [PATCH] mkdir: fix bug when -m's more generous than umask
Probl
Coreutils 8.32 (and possibly earlier) "mkdir -m ..." appears to
ignore parts of the mode specification. POSIX suggests that with -m
specified, the mode is "relative" to a=rwx. That implies a mode of "o-w"
should yield a mode of "rwxrwxr-x", and a mode of "o+w" should yield
"rwxrwxrwx". Instead:
$
