Last modified: 2013-09-02 20:22:52 UTC
https://www.mediawiki.org/wiki/Manual:$wgSquidServersNoPurge and CheckUser XFF should copy with users jumping from IPv6 to IPv4 and back and coping effectively with X-Forwarded-For addresses.
I'm not sure what this is about.
This is about application level proxies (e.g. Squids) that proxy IPv6 users to IPv4 or IPv4 users via IPv6.