Samba4 internal dns Failed DNS update

[steve]

> Hi Steve,
>
>> Not authoritative for 'some.domain', forwarding
>
> Ok, in a network trace, does the forwarder reply?

The forwarder is our ISP. In a browser, the site we have requested 
appears with frantic dns output. We then get the 'Not authoritative for 
abd.com forwarding.' message and dns messages stop. s4 messages still 
appear e.g. with kinit but very slowly. We then get:

../source4/dsdb/dns/dns_update.c:294: Failed DNS update - 
NT_STATUS_IO_TIMEOUT
And s4 has to be restarted.

>
> And you're sure restarting Samba isn't sufficient?
>

No. I was wrong. Restarting s4 gets us back up and running until we hit 
the forwarder again.

Any ideas?
Cheers,
Steve