Unable to set smbCreateMask on Yosemite server

Hello,

On an OSX server (Yosemite - 10.10.5) I want to use the smb file sharing to allow Windows (Win7) hosts to connect to shares. The Windows hosts must be able to simultaneously write to a file. When I run

serveradmin set sharing:sharePointList:_array_id:/Users/server/Documents/myshare:smbCreateMask = 0666

the newly set mask gets ignored.

Running serveradmin settings sharing shows that the setting remained the default 0644.

Similar for the smbDirectoryMask.

How can I set the permissions to remain at 0666?

Note1: Via the server GUI I allowed all users (even tried with Everyone) to have read/write permissions.

Note2: The Windows application is a Visual Foxpro app, it creates a table (file) that needs to be writable by different clients.

Note3: Also tried playing with setting smbUseOplocks and smbUseStrictLocking but these seem to be ignored.

Any help is appreciated. A similar setup with a Linux host running Samba yielded no issues.

kind regards