caller woes

test.pl

use strict;
use warnings;

my ($line1, $line2, $line3);

sub foo {
    (undef, undef, $line1) = caller(0);
}

$line2 = __LINE__ + 1;
foo(
    'f23' => {
        active     => 0,
        custom     => sub { 1 },
        notify_on  => 0,
        notify_for => 'active',
    },  
);
$line3 = __LINE__ - 1;

print "$line1 - $line2 - $line3\n";

__END__

$ perl test.pl
15 - 11 - 18

WTF?