Qmail vs PowerDNS

Hi all.  I've been running qmail with great success for many years.
I'm running gentoo with netqmail-1.06-r2; my network uses PowerDNS as
its local DNS server. 

I recently upgraded to pdns 4.  That's broken my qmail; now all
attempts to send result in the dreaded

CNAME_lookup_failed_temporarily._(#4.4.3)

I've debugged a bit.  Netqmail-1.06-r2 includes the big-dns patch, and
I verified that it was applied correctly.  I've run wireshark to
capture the network transactions, and nothing looks amiss.  I'm
getting valid responses, which are well under the 512-byte UDP limit
(though that shouldn't matter).  The problem is clearly pdns, as when
I change my resolver to some other server, qmail is perfectly happy.

What else should I look for?  What conditions other than oversize
packets would cause qmail to consistently faile the CNAME lookup?

Thanks in advance...