Xslate segfault when using nested blessed objects

gistfile1.pl

package helper;

sub new {
    my ($package, %args) = @_;
    return bless {
        %args
    }, 'helper';
}

sub test {
    my $self = shift;
    $self->{block} = bless { macro => pop }, 'test';
    return $self;
}

sub render {
    shift->{block}->{macro}->();
}

package main;

use Data::Dumper;
use Text::Xslate;

my $count = 0;
my $xslate = Text::Xslate->new(
    cache => 1,
    function => {
        count => sub {
            ++$count;
        }
    }
);

my $params = {
    c => helper->new
};

# works with cache 0/1/2
print $xslate->render('test.tx', $params );
# works with cache 0, undefined function with cache 1/2
print $xslate->render('test.tx', $params );
# works with cache 0, segfault for cache 1/2
print $xslate->render('test.tx', $params );