samba - Nov 2006 - NT_STATUS_NO_LOGON_SERVERS if Domain Controller is absent

I have my Samba 3.0.21c Linux Server as Domain member (security=ADS) so
that domain users can use the Samba Server as shared file server.
Everything works nice if the domain controller is present, e.g.

wbinfo -a DOMAIN\\donald%donald
plaintext password authentication succeeded
challenge/response password authentication succeeded

(this just simulates a Windows 2000 Client using the share which works
equally well)

Now I disconnect the domain controller and try the same:

wbinfo -a DOMAIN\\donald%donald
plaintext password authentication failed
error code was NT_STATUS_NO_LOGON_SERVERS (0xc000005e)
error messsage was: No logon servers
Could not authenticate user DOMAIN\donald%donald with plaintext password
challenge/response password authentication failed
error code was NT_STATUS_NO_LOGON_SERVERS (0xc000005e)
error messsage was: No logon servers
Could not authenticate user DOMAIN\donald with challenge/response

(this just simulates a Windows 2000 Client using the share which also
does not work with nearly the same error message on the Windows 2000 Client)

I have set-up winbind and kerberos in proper fashion (I hope), so what
else is wrong here or is it a bug in winbind?

I think that security=ADS is especially designed for my intended use
(backup file share if the domain controller is down). Or do I
misunderstand the Samba concept?

Note: I'm using passdb backend = tdbsam.