note 102605 rejected from datetime.sub by danbrown

Note Submitter: adam dot myszak at webchili dot pl 

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Why sub method wrong subtracts on that DateInterval example?

$actualDate = new DateTime('24-02-2011');
$oldDate = clone $actualDate;

$interval = new DateInterval('P1W2D'); // 1Week2Days
$actualDate->sub($interval);  
echo $actualDate->format('d-m-Y'); //   Why 22-02-2011 ?!

echo $oldDate->modify('-1 week -2 day')->format('d-m-Y'); // 15-02-2011