Comment 7 for bug 90681

I can confirm that I'm seeing the same bug with 32bit Feisty. The problem I am seeing is exactly the same as what has been described above - if the underlying interface has short DHCP lease, and it is renewed whilst the PPTP tunnel is enabled, then traffic will not be interrupted continue, but resolv.conf will be overwritten by dhclient.
I have applied the workaround (not updating resolv.conf when renewing leases) - though I can agree that is far from optimal. I was thinking of hacking the script so that it searches for a "ppp" interface in ifconfig to verify that a PPTP (or any VPN?) tunnel is up - and therefore do not force a update.
However, the more elegant solution would be if NM can detect and handle a DHCP renew (which isn't possible, as NM is simply a wrapper for dhclient and other underlying processes?) - and merge the new nameservers (in the case that they have changed since last lease? Unlikely, but possible?) with the existing VPN ones. This is elegant in that it will respect the USEPEERDNS option of the tunnel.
And in response to hq4ever - I believe you are experiencing another bug - one where NM does not respect the USEPEERDNS option - in a nutshell: if it is selected, then it works - if it's not, then NM replaces the existing resolv.conf with an empty one - which is not expected behaviour. See: https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/37239 ?