It turns out that question number one (why the eth0 stuff ended up in /etc/network/interfaces) was already covered by bug 388060 (an issue with casper).
As for the second issue however, about the valid interface (a wifi card) not showing, it still seems a valid problem. Some more digging around turned up that by using nm-tool, I could still see the wlan0 card. So this is either a problem solely in nm-applet, or in the combination of NetworkManager and nm-applet.
I will attach the output of nm-tool and nm-applet.
It turns out that question number one (why the eth0 stuff ended up in /etc/network/ interfaces) was already covered by bug 388060 (an issue with casper).
As for the second issue however, about the valid interface (a wifi card) not showing, it still seems a valid problem. Some more digging around turned up that by using nm-tool, I could still see the wlan0 card. So this is either a problem solely in nm-applet, or in the combination of NetworkManager and nm-applet.
I will attach the output of nm-tool and nm-applet.