Domains not resolving in Bind9, flush cache, clears issue.

Not sure if this is a bug, but I'm having wierd cache type issues on
Bind9.

I upgraded all our bind solaris8 servers from bind 8.2.3 to Bind9.2.2
(then 9.2.3). My 2 DNS servers that sit on the Internet after some
time (18+ hours) starts having issues resolving a couple extrenal
domains. Flush cache, and they would work again. I only have 2 that I
know of, it could be more.

When I would try to resolve these external domains having issues, it
just reports
domainname IN A

Thats it, no IP.

I did a trace before and after flushing the cache, also a db dump
before and after flushing cache. Theres nothing that looks out of
place in the dump, the trace shows it not resolving.

I reverted to bind8, and its resolving these domains again. Can't find
a common problem with the remote domains, and why Bind9 would just
fail after some hours.

Where should I go from here? I never submitted a bug for bind. Really
would like to use Bind9 for my Internet facing DNS servers.

Any ideas appreciated.