Description:
------------
Try to get Midnight of the first Weekday of a Weeknumber of a specific year:

$from = new DateTime();
$from->setTime(0, 0, 0);
$from->setISODate(2010, 28, 1); //Montag der 28ten Woche 2010
 
echo $from->format('d.m.Y H:i'); //A
echo $from->getTimestamp(); //B
echo date('Y-m-d H:i', $from->getTimestamp()); //C

The result is as expected, after adding an interval of 0 Days:
$from->add(new DateInterval('P0D'));

Expected result:
----------------
12.07.2010
1278885600
12.07.2010 00:00

Actual result:
--------------
12.07.2010
1291849200
29.05.2011 00:00