I had similar troubles with global destruction. I found this thread (Object reference disappearing during global destruction) and I thought I understood what was my error: to rely on the reference-count mechanism even during global destruction. Seeing the topic popping out again, I decided to do some experimentations in order to acquire a (?better) grasp on the subject. Here's the code:

use strict;
use warnings;

package Bar;
use Devel::Peek 'Dump';

sub new { bless [], shift }

sub bar { print "Hi, I'm a bar instance\n\n" }

sub dump 
{
    print "This is my ID card:\n";
    Dump( shift )
}

package Foo;

sub new 
{
    my $bar = Bar->new();

    bless { bar => $bar }, shift;
}

sub DESTROY 
{
    my $self = shift;
    $self->{ bar }->bar();
    $self->{ bar }->dump();
}

package main;

my $f = Foo->new();
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My expectation was to see a message like Can't call method "bar" on an undefined value with unpredictable frequence. I run the script several times, without warnings. Since this is a semidecidible issue, and I don't have all that time :), I ask if my understanding is correct, and further explanations if appropriate. Thank you.