Unfortunately, in a securely protected environment, you should disable IP version 6.  Ideally, disable it at the router level.

Because of the nature of the protocol, it can leak your true IP, even when VPN is solid.

Windows:

Just unselect it from the properties of a network interface.
Every other second, Windows 8 is constantly sending IPv4 packets with an IPv6 payload to win8.ipv6.microsoft.com.

Raspberry Pi:

sudo nano /etc/sysctl.conf

Enter the text:

net.ipv6.conf.all.disable_ipv6=1