Networking Locations Do Not Save Or Activate Correctly

This is in 70.4 Feisty.

I do not understand what happens when I save a System->Administrator->Network Location: My Acer 630 Travelmate laptop has a built-in eth0 and ath0 interface. Not knowing that I had a built-in wireless card, I have used a Cardbus card, and found I had an eth1 interface.

However, when I removed this card, and configured ath0, I got connectivity to my wireless router, but also have an eth1 back in /etc/network/interfaces. I'd like to know why and where there is documentation on how the network comes up.

Thanks.
Charles Norton