I think I got my leak narrowed down now, and it looks like Set::Object::Weak is the problem. I've written the following short test script:

use strict;
use warnings;
use Config;
use Test::More;
use Test::LeakTrace;
use Set::Object;

{
    package Foo;
    use Moose;
    1;
}

{
    no strict;
    note join ' ', map {$Config{$_}} qw(osname archname);
    note 'perl version ', $];
    note $_,'-',${"${_}::VERSION"} for qw{Moose Set::Object Test::Leak
+Trace};
}

my $set;
{
    $set = Set::Object->new;
    no_leaks_ok {
        {
            my $obj = Foo->new;
            $set->insert($obj);
            $set->remove($obj);
        }
    } 'Testing Set::Object for leaking';
}

{
    $set = Set::Object::Weak->new;
    no_leaks_ok {
        {
            my $obj = Foo->new;
            $set->insert($obj);
            $set->remove($obj);
        }
    } 'Testing Set::Object::Weak for leaking';
}

done_testing;
[download]

which gives me:

# linux x86_64-linux
# perl version 5.012004
# Moose-2.0202
# Set::Object-1.28
# Test::LeakTrace-0.13
ok 1 - Testing Set::Object for leaking (leaks 0 <= 0)
not ok 2 - Testing Set::Object::Weak for leaking (leaks 2 <= 0)
#   Failed test 'Testing Set::Object::Weak for leaking (leaks 2 <= 0)'
#   at Set_Object.t line 39.
#     '2'
#         <=
#     '0'
# leaked SCALAR(0xdad3a0) from Set_Object.t line 37.
#   36:            $set->insert($obj);
#   37:            $set->remove($obj);
#   38:        }
# SV = IV(0xdad398) at 0xdad3a0
#   REFCNT = 1
#   FLAGS = (IOK,pIOK)
#   IV = 0
# leaked ARRAY(0x1163cd0) from Set_Object.t line 36.
#   35:            my $obj = Foo->new;
#   36:            $set->insert($obj);
#   37:            $set->remove($obj);
# SV = PVAV(0x1394b00) at 0x1163cd0
#   REFCNT = 2
#   FLAGS = ()
#   ARRAY = 0x13ac740
#   FILL = 0
#   MAX = 3
#   ARYLEN = 0x0
#   FLAGS = (REAL)
#     Elt No. 0
#     SV = IV(0xdad398) at 0xdad3a0
#       REFCNT = 1
#       FLAGS = (IOK,pIOK)
#       IV = 0
1..2
# Looks like you failed 1 test of 2.
[download]

Can anyone else here verify this? And if not, could I kindly ask you to post the top 5 lines of the output (the os, arch and versions)?