I went through the same DNS leak problem.
At first I was able to solve it by adding the following to my .ovpn file and
manually running openvpn as root.
up /etc/openvpn/update-resolv-conf
down /etc/openvpn/update-resolv-conf
down-pre
This wasn't really an acceptable answer to me, because I wanted to use the
network manager applet.
Without adding the previous lines to my .ovpn files it turns out installing
the following packages and rebooting has eliminated the problem.
openresolv nscd unbound
Also, I used https://dnsleaktest.com/ to test for leaks and it can be used
without javascript.
