[Samba] Samba4: force user issue

[Steve Thompson]

I have a pair of CentOS 6.4 servers running Samba 4.0.3 as DC, and a set 
of member file servers, also CentOS 6, running Samba 3.6.9, joined to the 
Samba4 domain and running sssd. Birds sing and violins play. Everyone is
happy. Until...

A share definition such as:

[g_sysmgr]
     path = /fs/europa/g_sysmgr
     valid users = +sysgrp

works fine from both Linux and Windows clients, eg:

% smbclient //icse/g_sysmgr -U smt
Enter smt's password:
Domain=[EUROPA] OS=[Unix] Server=[Samba 3.6.9-151.el6]
smb: \>

The addition of the "force user" directive causes a failure (the user 
sysmgr is a member of the sysgrp group and owns all files and 
directories):

[g_sysmgr]
     path = /fs/europa/g_sysmgr
     valid users = +sysgrp
     force user = sysmgr

% smbclient //icse/g_sysmgr -U smt
Enter smt's password:
Domain=[EUROPA] OS=[Unix] Server=[Samba 3.6.9-151.el6]
tree connect failed: NT_STATUS_INTERNAL_DB_CORRUPTION

Qualifying the forced user name with the domain name has no effect.

There is _nothing_ in the Samba logs, even at level 10. Any ideas?

-Steve