Comment 22 for bug 1211110

I have found a work-around for 14.04 LTS. It's not the prettiest one but it works. When I started a vpn connection and then ran
ps -efwww | grep vpn
I could see that the openvpn is already called with flags "--script-security 2 --up /usr/lib/NetworkManager/nm-openvpn-service-openvpn-helper". So the following can be performed.

sudo cp /usr/lib/NetworkManager/nm-openvpn-service-openvpn-helper /usr/lib/NetworkManager/nm-openvpn-service-openvpn-helper.orig

sudo nano /usr/lib/NetworkManager/nm-openvpn-service-openvpn-helper
--- Add the following 3 lines to the file. ---
#!/bin/bash
/etc/openvpn/update-resolv-conf $@
/usr/lib/NetworkManager/nm-openvpn-service-openvpn-helper.orig $@
--- End---

sudo chmod +x /usr/lib/NetworkManager/nm-openvpn-service-openvpn-helper

Now here is the really ugly part. Since openvpn was not called with the --down flag, you should run the following command every single time the vpn connection is closed.
Change the device name according to your connection settings.

sudo script_type=down dev=tun0 /etc/openvpn/update-resolv-conf