Forwarding problem; Forward Last?

[Gabriel.Quennesson at fr.michelin.com]

Hi,
(needless to say I have been looking for the answer for days before 
posting here).

I am in the process of replacing Novell Netware's repackaged Bind by a 
standard Linux Bind build.
My setup is quite simple :

Bind is authoritative for sub.company.com. It uses 2 company.com 
forwarders (which doesn't know anything about our zone and/or network 
apart from a couple A records it holds for external sub.company.com 
access. That's stupid but that's how they do.)
There is an active directory, which is named -you guessed it allready- 
ad.sub.company.com. Bind is not a slave for that zone, it just holds a NS 
and it's glue record, as follow
ad      NS      ns.ad.sub.company.com.
ns.ad.sub.company.com.  A       192.168.0.1

My problem is the following: when my forwarders are down or undefined and 
I query Bind for a record in ad.company.com, it asks ns.ad.sub.company.com 
and answer with the right answer. (read : if the forwarders are defined 
but not reachable for some reasons, like FW blocking access, the cascading 
works).
However when Bind can reach the forwarders, it just asks them for records 
in ad domain; they answer with a no such domain and resolution stops 
there.

Reading Bind's documentation (and O'reilly's book, 5th edition) I am not 
missing anything obvious about delegation. It might have to do with my 
forwarder being unaware of my setup but I don't see quite how (and I can't 
do anything about it).
I have not tried to make bind a slave for the AD zone. I would like the 
above setup to work before trying other setups.

Any help would be apreciated,