Am Samstag, 25. Januar 2020 schrieb Florian Zieboll:
> very probably the parent directory is assigned to the "staff" group
> and has this bit set as well: It's called SGID-bit and recursively
> sets the group ID according to the directory owner instead of the
> current user - see man (1) chmod.

Hallo Florian,

yes, I just realised that is true for "/usr/local/"…

$ ls -l -d /usr/local
drwxrwsr-x 10 root staff 4096 Mai 31 2018 /usr/local

…so I concluded that to be a (debian) system standard and found that in
debian policy, see my previous mail.

Thank you.

Stefan