See this for some details:

http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=476579

Here is the basic test case, it segfaults, so I am going to leave it commented out. Basically it seems that there is some bad interaction between the ??{} construct that is used in the "parser" for type definitions and threading so probably the fix would involve removing the ??{} usage for something else.

use threads;

{ package Foo; use Moose; has "bar" => (is => 'rw', isa => "Str | Num"); }

my $thr = threads->create(sub {}); $thr->join();