Just to be clear, the 'Auto Ethernet' that I'm talking about is not the one you wrote in (and then removed from) your /etc/network/interfaces file - I meant the one that shows up in the GUI list of Wired network connections

YES. The only Wired Connection now available in the Network Connections applet is

HomeRunTuners.

that has a MAC address of: 00:18D:01:A7:99

and it is to connect automatically, available to all users and Method (of connecting) is

Link-Local only

Require IPv4 is UNCHECKED