BIND 8.4.6 trying IPv6 on system with no IPv6

I am seeing messages like:

Jan 30 22:07:33 ant named[655447]: ns_forw: sendto([2001:503:231d::2:30].53): Can't assign requested address

on my nameservers running BIND 8.4.6 (systems running Tru64 Unix 5.1B).
These systems are only configured for IPv4; why is BIND trying to make
requests via IPv6?
--
Chris Adams <cmadams@hiwaay.net>
Systems and Network Administrator - HiWAAY Internet Services
I don't speak for anybody but myself - that's enough trouble.