"Bad UDP checksum" problems

I am setting up some virtual servers using Fedora 8 and Xen. (I
cannot use Fedora 9 because it doesn't support running as a Xen
Dom0.) The kernel version is 2.6.21.7-3.fc8xen.

The network interface "card" is a Marvell 88E8053 PCI-E GigE (rev
15) that is built-in to the motherboard. I am using the sky2
driver kernel module.

Here's my problem. After setting up the system, I noticed that DNS
name resolution was not working; the queries ("host XXX" or
"nslookup XXX") were timing out.

I ran tcpdump on the box where my DNS server is running, and it
reports "bad udp cksum" for the packets received from the client
system.

Then, on a lark, I tried "host -T XXX" and that worked. Fine. But
then I realized that UDP-based queries were now working too; the
UDP checksum problems had magically gone away!

Anyone have any ideas about what might be going on and/or what I
can do to fix it (other than including a "host -T XXX" in my
network initialization scripts).

MV
P.S. If it matters, I am not using NetworkManager, I am using
traditional init network scripts.

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