samba File permisions not as expected after upgrade of samba

samba File permisions not as expected after upgrade of samba
Redhat 6.6 and Redhat 6.7

We updated yesterday to the following and now we see the following

samba-client-3.6.23-20.el6.x86_64
samba-winbind-3.6.23-20.el6.x86_64
samba-winbind-clients-3.6.23-20.el6.x86_64
samba-common-3.6.23-20.el6.x86_64
samba-3.6.23-20.el6.x86_64

With the following in smb.conf
[docarchive]
path = /opt/shares/users
writable = yes
public = yes
create mask = 664
directory mask = 0777
force group = users

From the windows server when a file is created is now reports
-rw-rw-r-- 1 charvey BUILTIN\users 0 Sep 9 11:51 CHarvey Test Doc3.txt

however on this version we see
samba-client-3.6.23-14.el6_6.x86_64
samba-common-3.6.23-14.el6_6.x86_64
samba-winbind-3.6.23-14.el6_6.x86_64
samba-3.6.23-14.el6_6.x86_64
samba-winbind-clients-3.6.23-14.el6_6.x86_64

-rw-rw-r-- 1 charvey users 0 Sep 9 11:44 CHarvey Live Test Doc.txt

We expect that files created with the force group = users option set in samba are created with the group set to "users" and not "BUILTIN\users"

Any one know why this has happened?