Thanks for that suggestion. I don't believe I did anything on purpose to set up different locations, but I'll check. I'm assuming you're referring to this.

The other thing that Google searches told me was that if I had multiple wifi networks connected to the same LAN, it might get confused in the routing and might prioritize the Wifi because it thinks it's a more direct route. I don't think that's what's happening with me either, or at least, it shouldn't be.

The Wifi router that I'm using is also my house's DHCP server, and everything in the house plugs into the Wifi router's built-in ethernet switch. The cable modem is upstream from the Wifi router, and we don't use the Wifi that's built into the cable modem. There are other ethernet switches in various places in the house, but they're just dumb switches, not routers. Still, if the Mac can detect that there are some switches in the chain, and it's trying to be clever about it, it might indeed think that the Wifi is the shorter link... Between my Mac and the router, there are two gigabit-ethernet switches: One in my office/studio that the Mac is plugged into (along with all my other gear in the office), and one in the closet just before the Wifi router (the rest of the ethernet ports in the house connect to that switch in the closet too).