force create mode not enforced on newly created files

[Dariusz Gadomski]

Samba version used:
4.3.9+dfsg-0ubuntu0.16.04.2

Steps to reproduce:
1. Configure a samba share with inherited permissions:
[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

2. Create a directory under the share:
cd /srv/share1; mkdir modes && chmod 2770 modes

3. Connect with a Windows client and create some files and directories in the new directory:
New text document.txt*
test.txt
New folder*
test

Entries marked with * have their default names (picked by Windows) untouched.

What is expected?
All files and directories have permissions set according to share configuration.

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.