PHP日历错误的开始日期为2015年8月

我从about.com获得了上述代码。除了2015年8月，一切都很顺利。开始日期应该是星期六，但是日历显示的是星期一。到目前为止，我检查过的其他月份都是正确的。

提示吗?

<?php
function calendar() {
    date_default_timezone_set('UTC');
    $date = time(); // it was removed orginally.
    if (ISSET($_REQUEST['emonth'])&& ISSET($_REQUEST['eyear'])){
        $month = $_REQUEST['emonth'];
        $year = $_REQUEST['eyear'];
    } else {
    $month = date('m', $date);
    $year = date('Y', $date);
    }
    $first_day = mktime(0,0,0,$month, 1, $year);
    echo date('D', $first_day); 
    $title = date('F', $first_day);
    $day_of_week = date('D', $first_day);
    switch($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 "Sar": $blank = 6; break;
    }
    $days_in_month = cal_days_in_month(0, $month, $year);
        echo '<table class="event">
                    <tr>
                        <td colspan="7">'.$title.'-'.$year.'</td>
                    </tr><tr>
                        <th>Sun</th><th>Mon</th><th>Tue</th><th>Wed</th><th>Thu</th><th>Fri</th><th>Sat</th>
                    </tr>';
    $day_count = 1;
    echo '<tr>';
    while ($blank > 0) {
        echo '<td></td>';
        $blank = $blank-1;
        $day_count++;
    }
    $day_num = 1;
    while ($day_num <= $days_in_month){
        echo "<td>$day_num</td>";
        $day_num++;
        $day_count++;
        if ($day_count > 7) {
            echo '</tr><tr>';
            $day_count = 1;
            while ($day_count > 1 && $day_count <= 7) {
                echo '<td></td>';
                $day_count++;
            }
        }
    }
                echo '</tr>
                            </table>';
}
calendar();
?>

开关箱中出现了Sar的错别字，而不是Sat。因为它在我检查的大部分月份都有效，所以我忽略了它。

谢谢人