[Samba] file locking failure

[steve]

4.0.7 DC, 4.0.7 fileserver, with openSUSE, w7 and xp clients.
cifs-utils 6.1 on Linux.

Hi
I have set:
kernel oplocks = yes
on the fileserver

If the xp client opens a file using e.g. Notepad, the opensuse client
can edit it at the same time and vica versa.

If I open the same file on each client using Libre Office then fine, it
works (I think because of Libre Office, not samba)

How do I get locking to work outside Libre Office. Nothing else seems to
work.
Cheers,
Steve