Description:
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While using date("d", mktime(0,0,0,11+1,0,2008); to retrieve the number of days in November I continually have 29 returned. While December and other months are correct.

Reproduce code:
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foreach($this->vacationDays as $entry) {
    $nowdate = split("/", $entry[1]);
    $ourDate = mktime(0,0,0,(int)$nowdate[0],(int)$nowdate[1],(int)$nowdate[2]);
    $ourMonth = date("M", $ourDate);
    $ourDay	= date("D", $ourDate);
    $ourYear = date("o", $ourDate);
    $firstDayOfMonth = mktime(0,0,0, $nowdate[0], 1 , $nowdate[2]);
    $firstDayInMonth = date("D", $firstDayOfMonth);
    $daysInMonth = date("d", mktime(0,0,0,(int)($nowdate[0]+1), 0, (int)$nowdate[2]));
    $day_of_week = $firstDayInMonth;
								
    switch($day_of_week) {
	case "Sun": $blank = 0; break;
	case "Mon": $blank = 1; break;
	case "Tue": $blank = 2; break;
	case "Wed": $blank = 3; break;
	case "Thu": $blank = 4; break;
	case "Fri": $blank = 5; break;
	case "Sat": $blank = 6; break;
    }
				
    if(isset($currentMonth) && $ourMonth != $currentMonth) {
	$currentMonth = $ourMonth;
			
	$this->startCalendarMonth($ourMonth, $ourYear);
		
	$day_count = $this->shootBlanks($blank);
		
        for($day_num = 1; $day_num <= $daysInMonth; $day_num++)
        {							
            echo "<td>$day_num</td>";
            $day_count++;
            if($day_count > 7) {
	        echo "</tr>\n    <tr>";
	        $day_count = 1;
            }
        }
	$this->endCalendar();
    }


Expected result:
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The expected result is that November 2008 would return 30 days and December 2008 return 31 days.  

Actual result:
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The current result is Nov 2008 returns 29 days and December 2008 returns 31.  Clearly the problem is with November.