On line 60 of etc/network, there is the line
/sbin/route add default dev $DEVICE
which presumably adds the current device as the default gateway, when dhcp is enabled.
When I insert my 3com ethernet card, configured as a static interface in network.opts, it works properly as default route. When I plug in my wavelan card, it takes over as default route, which means it knocks out default route for the ethernet, and makes it go over the wavelan. Right now, I am not near a access point, so dhclient finds nothing on the wavelan and goes to sleep. But the card is configured as default route, which I don't want. When I comment out the route add line in etc/network, it works correctly. Is the line necessary? Doesn't dhclient automatically add the route as necessary? Seems like it, check out /etc/dhclient-script.
I am running Debian woody on x86.