Grepping both IO::Socket 1.31 and IO::Socket 1.36 for "INET6" yields no results for me.

Can you show us a short program that reproduces your problem and shows that IO::Socket loads IO:;:Socket::INET6?

#!perl -w
use strict;
use Data::Dumper;
use IO::Socket;

# whatever you need to do to make the error message/warning show up in
+ INET6.pm

print Dumper \%INC;
[download]

Of course, you can always try to rename IO/Socket/INET6.pm ;)