Qmail vs PowerDNS

Update:  I figured out the misconfiguration at the pdns level.
Essentially, pdns has a configurable UDP truncation size, and the
default is bigger than a regular datagram.  Setting it to a lower
value causes value causes the server to say "truncated" and the
resolver to fall back to TCP.  That makes it all work correctly.

If anybody out there is running pdns and wants details of my config,
I'm happy to oblige.

Thanks all for your input and advice.