PDO事务处理不能保持一致性

直接上代码：

<?php
require_once 'db_const.php';
require_once 'helperPub.php';

//测试存储过程的事务
//http://localhost/API_WMS/WMS_BatchTest.php

echo 'Hello' . PHP_EOL;
$ret = BatchTest();

echo json_encode($ret, JSON_UNESCAPED_UNICODE);

function BatchTest()
{
    $ret_value = array();
    echo '1' . PHP_EOL;
    
    $db = new PDO(STR_CONN, DB_USER, DB_PASS);
    $db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $db->beginTransaction();    
    try {

        $sql = 'execute procedure PROC_S1;';
        $statement = $db->prepare($sql);        
        $ret = $statement->execute();
        if(! $ret)
        {
            throw new Exception("PROC_S1");            
        }  
        echo '2' . PHP_EOL;
        $sql = 'execute procedure PROC_S2';
        $statement = $db->prepare($sql);        
        $ret = $statement->execute();
        if(! $ret)
        {
            throw new Exception("PROC_S2");            
        }    
        $db->commit();            
        unset($statement);
        unset($db); 
        $ret_value['CODE'] = 0;
        $ret_value['MSG'] = 'OK';
        $ret_value['DATA'] = '123';
        return $ret_value;
    }
    catch (Exception $e)
    {
        echo '3' . PHP_EOL;
        $db->rollBack();
        echo '4' . PHP_EOL;
        $ret_value['CODE'] = 1;
        $msg = change_error_msg( $e->getMessage());
        $ret_value['MSG'] = $msg;
        $ret_value['DATA'] = "";
        return $ret_value;
    }
}

?>

当存储过程PROC_S2中抛出异常时，PDO虽然执行了回滚，但PROC_S1操作的内容并没有发生回滚。数据库用的是FireBird。可能是FirdBird的PDO实现有BUG。