INSIST(evDo(ev, "handle_needs") != -1) in ns_main.c error after upgrading

I upgraded from 8.3.4 to 8.4.4 on a Tru64 V5.1B (decunix) machine.

After the upgrade the name server started without a problem and ran for
about 45 mninutes and then died. The log contained these messages, just
before named stopped:

May 11 16:20:39 dns3 named[93844]: ns_main.c:4439: INSIST(evDo(ev,
"handle_needs") != -1
): No such file or directory failed.
May 11 16:20:39 dns3 named[93844]: ns_main.c:4439: INSIST(evDo(ev,
"handle_needs") != -1
): No such file or directory failed.

I restarted the ns, and the same thing happened after another 30-45 min.

I've since downgraded back to 8.3.4 and all is ok again.

Any ideas?

Thanks a lot