How immutable is immutable?

immutable.pl

#!/usr/bin/env perl

use strict;
use warnings;
use v5.10;

use Class::MOP;

my $tc_meta = Class::MOP::Class->initialize("TestClass");
$tc_meta->make_immutable(inline_constructor => 0);

eval {
    $tc_meta->add_method("cm_test", sub { say "Not so immutable" });
    my $test1 = TestClass->new;
    $test1->cm_test;
} or warn "Can not add method the Class::MOP way";

eval {
    no strict 'refs';
    *{"TestClass::of_test"} = sub { my $self = shift; say "Not so immutable" };
    my $test2 = TestClass->new;
    $test2->of_test;
    use strict;
} or warn "Can not add method the old fashioned way";

package TestClass;

sub new {
    return bless({}, shift);
}

When doing evals of the form eval { ... } or warn "blah" shouldn't you have a true value as the last expression in the eval block? Like so: eval { ...; 1; } or warn "blah"