netware 6 sp2 server running named 5.10.09

Certain clients, both NT and 2k:
*intermittently loose their ability to resolve internal DNS names
*can still resolve external names
*receive dns server addresses via Novell dhcp, lease time 14 days
*ipconfig /all shows correct info, including dns server addresses
*can ping dns servers (and any others) by ip address
*release/renew resolves the problem... for a few hours

We're going to put a Sniffer on a machine that's having the symptom,
in the mean time I thought I'd post this.

Ideas? Thanks!