8.2.3-REL and Slave Zone Problem

[Markus Becker]

Hi,
maybe this is an FAQ, but I'm experiencing the following Problem
w/ BIND 8.2.3-REL:
The Server in question -let's name him dns_a- shall be slave for sub-zone 
local.mydomain.com. All other requests are forwarded (via the
forward-statement) to a server dns_b, which itself is only a forwarder.
A third host, dns_c, is master for local.mydomain.com as well as mydomain.com.
What happens is this: Requests for local.mydomain.com are handled locally,
but dns_a does not update himself for his slave-domain, because 
dns_b (which is not within my reach) returns a "non authoritative for
zone local.mydomain.com". The same configuration however DID work on
another machine which used to be dns_a and had a BIND 8.2.2 installed.
Could this be a bug or is it just a mistake by myself ?
What would you suggest to solve this problem ??
Thanks in advance

Markus Becker