Comment 13 for bug 262152

Yes, and in some cases it's the policy of the network administrator to strictly forbid connecting to both wired and wireless in the same building. If they are different subnets, you have the potential to act as a network bridge (yes I know this takes effort, but the potential is still there). We had several cases of folks getting their MAC's quickly banned when a dual connection was detected.

I understand the NM dev's position on the "auto connect"; that behavior was probably a major chunk of work (and is great!). However, we now have this regression. A quick solution would be to add an option to each connection to say something like "disable this connection when another is active"; then tick it for your wireless connection(s). Or, the reverse might make more sense: "disconnect all other connections when this is active", and tick it for wired. A more complete solution would be to have pools of connections, or locations, and add whatever connections you'd like active in the pool. Then, you connect to pools/locations instead of individual connections. Bonus, a hook could be provided to execute custom scripts on activation of each pool/location.

Maybe someone with time (i wish that was me) can patch NM, then Ubuntu might accept it and we can close this bug.