php dateinterval comparation bug

dateinterval-bug.php

<?php

function printComparationResults($interval, $intervalWeek) {
  if ($interval < $intervalWeek ) {
    echo "interval is smaller\n";
  }

  if ($interval == $intervalWeek ) {
    echo "intervals are equals\n";
  }

  if ($interval > $intervalWeek ) {
    echo "interval is bigger\n";
  }
echo "------------------------\n";
}

$yesterday = new DateTime('2013-12-11 12:40:00');
$now = new DateTime('2013-12-12 12:40:00');

$intervalWeek = DateInterval::createfromdatestring('1 week');
$interval = $now->diff($yesterday);

printComparationResults($interval, $intervalWeek);
$a = var_export($interval, true);
printComparationResults($interval, $intervalWeek);
$b = var_export($intervalWeek, true);
printComparationResults($interval, $intervalWeek);

/* result in PHP 5.4.21 and PHP 5.5.5 */

intervals are equals
------------------------
interval is bigger
------------------------
interval is smaller
------------------------