This was mentioned in ticket:1111#comment:5
You can only add ipv4 addresses to the tracking exclusion list. Please add support for excluding ipv6 addresses as well.
Please consider contributing this enhancement as pull request :) http://piwik.org/participate/contributing-with-git/
I think IPv6 addresses are supported for quite a while (at least since https://github.com/matomo-org/component-network/pull/3)