It is not only related to docker… it’s related to my Synology NFS Server i guess.
I reproduce the issue with the following workflow :
root@Seafile:~# touch test
root@Seafile:~# chmod 640 test
root@Seafile:~# cp test /mnt/Seafile/
root@Seafile:~# ls -la /mnt/Seafile/
total 24
drwxrwxrwx 5 nuc nogroup 4096 Oct 12 22:04 .
drwxr-xr-x 4 root root 4096 Oct 10 00:23 ..
drwxrwxrwx 3 1024 users 4096 Oct 12 22:00 data
drwxrwxrwx 3 1024 users 4096 Oct 12 21:51 Seafile
-rw-r----- 1 1024 users 0 Oct 12 22:04 test
root@Seafile:~# mv test /mnt/Seafile/test2
mv: failed to preserve ownership for '/mnt/Seafile/test2': Operation not permitted