With the following share definition: [share1] path = /srv/share1 browseable = yes read only = no guest ok = no create mask = 0770 force create mode = 0660 directory mask = 2770 force directory mode = 2770 I create a directory: cd /srv/share1; mkdir modes && chmod 2770 modes There from a Windows client I connect to the share and create some files & directories: New text document.txt* test.txt New folder* test Entries marked with * have their default names (picked by Windows) untouched. Here is what happens: └── [drwxrws---] ./modes ├── [-rwxr-----] ./modes/New text document.txt ├── [drwxrws---] ./modes/New folder ├── [drwxrws---] ./modes/test └── [-rwxrw----] ./modes/test.txt Despite force create mode the "New text document.txt" does not have group-write permission, while another file with custom name has the permissions set as desired. When I rename "New text document.txt" to anything else the permissions are fixed immediately: └── [-rwxrw----] ./modes/test2.txt This was not observable with Samba 4.1.6.