I have a SerNet Samba 4.0.8 AD DC running on CentOS 6.4 (newdc) 
replicating from a W2K3 DC (olddc).  newdc also has a test share.

I'm experiencing something strange whereby chmod and then an attempted 
file save causes a shared file to become zero bytes (despite the save 
not being blank, and also being denied):

At olddc:

1) open \\newdc\testshare\yay.txt


At newdc:

$ ls -l
total 8
-rw-rw-rw-. 1 me  me  9 Aug 20 10:59 yay.txt
$ cat yay.txt
It works!$ chmod 664 yay.txt


At olddc:

1) add a space to yay.txt and attempt to save.  popup:

---------------------------
TextPad
---------------------------
Access to \\newdc\testshare\yay.txt was denied.
---------------------------
OK
---------------------------

2) (optional) click OK to close the popup

At newdc*:

$ ls -l
total 4
-rw-rw-r--. 1 kev kev 0 Aug 20 11:12 yay.txt

* Alternatively, without touching newdc, I can shift focus from the 
TextPad window and back to it, and it will say that the file has 
changed.  If I choose to reload it, it's now blank.


Isn't this a bug?  I would expect a write that fails due to lack of 
write permissions to not actually affect the content of the file.

I have SELinux disabled.

I just experienced this in a similar fashion after upgrading to Sernet Samba 4.0.9.  On OLDDC, I made a change to \\olddc\netlogon\logon.cmd , then in Windows Explorer, attempted to copy that file and past it at \\newdc\netlogon\logon.cmd.  It gave me an access denied error, and then overwrote my logon.cmd with a zero-byte file!  I then took ownership of the netlogon directory on newdc (still from the Windows 2k3 UI) and I was able to paste the file correctly, whew.

It's possible I have something misconfigured, but IMO one shouldn't be able to configure things this way (i.e., when would this ever be a desirable result?)

Anyway my configuration for these shares is:

[netlogon]
        path = /var/lib/samba/sysvol/mydom.lan/scripts
        read only = No

[mytest]
        path = /home/srv/samba-test-share
        read only = No
        force create mode = 0777
        force directory mode = 0777

Thanks,
Kev