try-catch块不适用于pdo语句和foreach

最近我鼓励在PHP代码中出现奇怪的错误。这就像在将PDOStatement对象与foreach(){}一起使用时省略了内部try{}catch(){}块。这是我触发这种行为的测试代码：

<?php
/* 
// THIS WORKS AS EXPECTED, JUST UNCOMMENT
try{
    for($i = 0; $i < 3; $i++){
        try{
            echo "'nTHROWING EXCEPTION'n'n";
            throw new Exception("AAAAAAAAAAAAAAAAAAAAAAAAA");
            echo "EXCETION THROWN (SHOULD NOT SHOW)'n";
        }catch(Exception $err){
            echo "========= INNER CATCH ========='n";
            echo $err->getMessage() . "'n";
        }
    }
}catch(Exception $e){
    echo "=========== OUTER CATCH ==========='n";
    die($e->getMessage() . "'n");
}
die("'nEVERYTHING OK'n");
*/
$dsn = "mysql:dbname=test_pdo;host=localhost";
try {
    $dbh = new PDO($dsn, 'root', "", array(PDO::MYSQL_ATTR_INIT_COMMAND => "SET NAMES utf8"));
    $dbh->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
    $dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $dbh->exec("
    CREATE TABLE IF NOT EXISTS `test` (
    `id` int(10) unsigned NOT NULL,
    `name` varchar(255) NOT NULL,
    PRIMARY KEY (`id`),
    UNIQUE KEY `name` (`name`)
    ) ENGINE=InnoDB DEFAULT CHARSET=utf8;
    ");
    $dbh->exec("TRUNCATE test");
    $dbh->exec("
    INSERT INTO test (id, name) VALUES 
    (1, 'JOHN DOE 1'), (2, 'JOHN DOE 2'), 
    (3, 'JOHN DOE 3'), (4, 'JOHN DOE 4')
    ");
    echo "'nRECORDS CREATED'n";
    $sth = $dbh->prepare("SELECT id FROM test WHERE id = ?");
    foreach(array(2, 3, 4) as $id){
        $sth->execute(array($id));
        $i = 0;
        foreach($sth as $row){
            $num = $row['id'] - 1;
            // this sql should throw 2300 error duplicate key
            $sql = "UPDATE test SET name = 'JOHN DOE $num' WHERE id = {$row['id']}";
            try{
                echo "'nSENDING QUERY: $sql'n'n";
                $dbh->exec($sql);
            }catch(Exception $err){
                $code = $err->getCode();
                $msg = $err->getMessage();
                //duplicate key error?
                if($err->getCode() != "23000"){
                    echo "THROWING EXCEPTION FROM INNER CATCH.'n ERROR CODE: $code'n";
                    throw $err;
                }
                echo <<<TXT
============ GOOD CATCH ============
ERROR CODE: $code
ERROR MSG: $msg
SQL: $sql

TXT;
            }
        }
    }
}catch(Exception $e){
    $code = $e->getCode();
    $msg = $e->getMessage();
    echo <<<TXT
============ WRONG CATCH ===========
ERROR CODE: $code
ERROR MSG: $msg

TXT;
}

这在我的本地主机（PHP 5.3.6-13ubuntu3.6和Suhosin Patch（cli））和服务器（PHP 5.2.17）上输出类似的内容：

RECORDS CREATED
SENDING QUERY: UPDATE test SET name = 'JOHN DOE 1' WHERE id = 2
============ GOOD CATCH ============
ERROR CODE: 23000
ERROR MSG: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'JOHN DOE 1' for key 'name'
SQL: UPDATE test SET name = 'JOHN DOE 1' WHERE id = 2
============ WRONG CATCH ===========
ERROR CODE: 23000
ERROR MSG: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'JOHN DOE 1' for key 'name'

不知道为什么，但当我将foreach($sth as $row){更改为foreach($sth->fetchAll() as $row){时，一切都如预期：

RECORDS CREATED
SENDING QUERY: UPDATE test SET name = 'JOHN DOE 1' WHERE id = 2
============ GOOD CATCH ============
ERROR CODE: 23000
ERROR MSG: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'JOHN DOE 1' for key 'name'
SQL: UPDATE test SET name = 'JOHN DOE 1' WHERE id = 2

SENDING QUERY: UPDATE test SET name = 'JOHN DOE 2' WHERE id = 3
============ GOOD CATCH ============
ERROR CODE: 23000
ERROR MSG: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'JOHN DOE 2' for key 'name'
SQL: UPDATE test SET name = 'JOHN DOE 2' WHERE id = 3

SENDING QUERY: UPDATE test SET name = 'JOHN DOE 3' WHERE id = 4
============ GOOD CATCH ============
ERROR CODE: 23000
ERROR MSG: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'JOHN DOE 3' for key 'name'
SQL: UPDATE test SET name = 'JOHN DOE 3' WHERE id = 4

我是发现了错误还是做错了什么？有人能证实这种行为吗？Thx

//编辑

将PHP版本升级到5.3.10似乎可以解决这个问题。寻求帮助。。。