Every time I use bluetooth to tether (via DUN) to my Samsung phone the DNS information is forced into other connections (WIFI/Ethernet). Turning off the connection (and bluetooth) doesn't seem to fix it. If I use the connection manager and try to set my wifi connection to automatic it always pulls in the old phone DNS addresses. I can set the DNS manually which works when there's no proxy (only because I don't know the IP of the proxy to set the DNS to manually).
I can't figure out a way to auto configure DNS, the connection always ends up with the phone's DNS settings.
By the way, I had the same problem with a GSM USB dongle. The only way I could fix it was to uninstall the GSM driver. However with bluetooth tethering nothing shows up in the connection manager.
The IP will auto-configure, but the DNS never will. Any thoughts? (I've tried service networking restart, service network-manager restart, dhclient (-r and again without)) Rebooting, etc.
EDIT: Using Linux ubuntu 3.2.0-48-generic #74-Ubuntu SMP Thu Jun 6 19:45:16 UTC 2013 i686 i686 i386 GNU/Linux