Comment 15 for bug 90681

The behaviour varies because the resolver configuration file gets overwritten each time the lease is renewed. There are two contending parties: the local provider and the remote provider; which party wins depends on which lease expires earlier (more often). I agree it is unmanageable; indeed, the resolver configuration should be a union of information provided by all sources, not just one of them taken on last-wins basis, and there must be an option to deny all influence on the resolver configuration from remote connections, or preferably connection-wise (it slows down the resolver a lot if it goes through the tunnel for all queries).
It would be much more pernicious if the default gateway were replaced in the same way; fortunately it is not the case.