I can't solve the problem, but that info turned out to be sufficient for me to guess where to poke. I can reproduce a segfault in just 7 lines of code.

File: mx_segfault.pl

use lib '.';
use Demo;
[download]

File: Demo.pm

package Demo;
use MooseX::Extended;
require Stuff;
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File: Stuff.pm

package Stuff;
use MooseX::Extended;
[download]

With this code, perl -wc mx_segfault.pl segfaults, and valgrind throws a 455-line tantrum.