DNS Leak is always a problem of your OS and never VPN providers fault!
You have to follow some rules to gain maximum protection against DNS Leaks with oVPN or any VPN!
DNS Leaks with VPN will occur if your OS requests IP and DNS from DHCP which is normal router/modem setting or you're using your router as static nameserver.
Why does DNS Leak happen with oVPN?
Your router forwards DNS queries to your ISP: so you can browse the WWW.
oVPN pushs internal DNS (172.16.32.1) to your openVPN TUN/TAP adapter, but with DHCP enabled your OS knows 2 DNS now: (Router) + (oVPN DNS).
Your OS sends DNS queries to all known DNS and even with connected oVPN your OS will send DNS queries directly to your router/ISP!
Set DNS on all Interfaces (LAN, WLAN/WIFI) and use our oVPN internal DNS: 172.16.32.1
Linux Users should replace content of "/etc/resolv.conf" with "nameserver 172.16.32.1" or set your network-manager to use DNS: 172.16.32.1