Comment 1 for bug 1499739

Unfortunately this is the way NetworkManager works. It's goal is to establish a network connection using the highest priority device and connection available. Success is defined as connection established and networking configuration successful ( ie. IP address assigned, routing table setup, ... ).

NetworkManager does support a feature called 'connectivity checking', see the following blog post ( look for the conf directive: "[connectivity]" ):

https://blogs.gnome.org/dcbw/2015/02/16/networkmanager-for-administrators-part-1/

That said, it's currently disabled as when first tested on Ubuntu, it didn't work that reliably, so it was never enabled by default. It's a bit too late to make this change in wily, so maybe this is something that should be explored for 16.04? That said, if you feel like this is important enough, please raise it with someone from the product team.