Comment 12 for bug 262152

There is a similar report of Fedora: https://bugzilla.redhat.com/show_bug.cgi?id=454955
There the devs say it is intended behavior for NM to connect to all networks that are marked "auto connect".
However, I think there should be an option to only allow one connection at a time, with some priorities (eg. wired has more priority than wireless). There are clearly situations were you do not want to have two connections at the same time, like, eg., the one mentioned by Michael Milligan above. Moreover there is a cognitive issue because nm-applet doesn't seem to know what icon to display: a strenght meter or a wire; sometimes it is one and sometimes the other.