Actually, the issue does not appear to be quite fixed. So when I changed the settings, rebooted the machine, correct /etc/resolv.conf has been created by netconfig - I'm using 'Auto eth0' for network connection. However this morning when I resumed the machine from suspend-to-ram, when network manager reconnected, /etc/resolv.conf has been suddenly replaced by the problematic one (i.e., the one directly generated by NM).