Glue Cacheing 8.3.1 vs 8.3.3

[Tim Maestas]

I have a server, master for the root zone, with the following delegation
and glue:

domain.com.	IN	NS	server1.domain.com.
		IN	NS	server2.domain.com.
server1.domain.com.	IN	A	10.0.0.1
server2.domain.com.	IN	A	10.0.0.2

However, on the authoritative servers for domain.com, server1 and server2
do not exist in domain.com.  They actually exist in sub.domain.com.  The
IP addresses are correct however, 10.0.0.1 and 10.0.0.2.

On my 8.3.1 servers, resolution for hosts in domain.com worked fine with
the above situation.  Examining a cache dump, it appears that the glue was
cached from the root server.  Upon upgrading some servers to 8.3.3,
resolution broke for hosts in domain.com.  The servers would return
SERVFAIL.  Looking in their cache, only the NS records from the root
server were cached.  There were negative cache entries from 10.0.0.1 for
server1.domain.com and server2.domain.com in cache as well.  So, the 8.3.3
servers had NS records cached that pointed to A records that were cached
as
NXDOMAIN.  My question is, what specifically changed from 8.3.1 to 8.3.3
in relation to glue cacheing?  A query to the 8.3.3 servers for the NS
records for domain.com seemed to result in a query to the root servers,
then a query to 10.0.0.1 for server1.domain.com and server2.domain.com
which resulted in the negative cache entries, leading to the SERVFAIL on
subsequent queries for hosts in domain.com.  The obvious fix was to fix
the delegation on the root servers to correctly reference
server1.sub.domain.com  and server2.sub.domain.com with appropriate glue,
but I am curious to completely understand the behavior.

Thanks.

-Tim