DNS via Linksys ADSL2MUE modem not working properly

[Neil Woolford]

First of all, I *don't* need suggestions for workarounds, as I already have a
working fix for this problem, based on editing /etc/dhcp3/dhcp.conf as advised
at https://wiki.ubuntu.com/StaticDnsWithDhcp.  However I would like to know why
the system is not working as I would expect, and whether this can be fixed: 
indeed, if it is a bug, then suggestions as to where to file would be welcome...
 If I've missed the point about some aspect of networking, then pointers to
enlightenment would also be welcome...

I connect to broadband via a Linksys ADSL2MUE modem, at 192.168.1.1.  The modem
is set to provide DHCP and correctly sets itself to the DNS address settings of
my ISP.  When connected to my ancient laptop running windows 98SE, the modem
provides a reliable DNS service under its own address (192.168.1.1).

Under Ubuntu (Hoary, Breezy and Dapper so far) the DNS Server is automatically
set  to that address (192.168.1.1).  However, applications such as Firefox and
Update Manager just hang as they appear not to be able to access any DNS Server.
 If I run nslookup from a terminal I do get sensible information about numeric
IP addresses, from the DNS Server at 192.168.1.1, so it does appear to be
present and active.  As I mentioned before, my Windows machine has no trouble
using it.

I do have a workaround, by setting prepending of my ISP's DNS addresses in
dhcp.conf, but I would really prefer not to have to do this.

Has anyone any idea what is happening here?  I'm no expert on networking issues
- suggestions for further diagnostic tests to try would be very welcome.

Neil