MySQL_Session.cpp:2452:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG

[beebol]

proxysql version:
ProxySQL version 1.4.15-1-g61bc777, codename Truls

2020-05-20 15:59:41 MySQL_Session.cpp:2887:handler(): [ERROR] Detected a broken connection during query on (1,10.200.131.4,3306) , FD (Conn:43 , MyDS:43) : 2057, The number of parameters in bound buffers differs from number of columns in resultset
2020-05-20 15:59:43 MySQL_PreparedStatement.cpp:315:update_metadata(): [WARNING] Updating metadata for stmt 1 , user sbtest_rw, query SELECT * FROM sbtest1 WHERE id =?
2020-05-20 15:59:43 MySQL_Session.cpp:2452:handler(): [ERROR] RECEIVED AN UNKNOWN COMMAND: 28 -- PLEASE REPORT A BUG

replay process：
prepare.php

<?php
$dsn      = 'mysql:dbname=sbtest;host=10.200.131.3;port=6033';
$user     = 'sbtest_rw';
$password = 'sbtest_rw_123';

try {
    $params = [
        PDO::MYSQL_ATTR_INIT_COMMAND => "set names utf8", 
        PDO::ATTR_EMULATE_PREPARES   => false, 
    ];
    $db = new PDO($dsn, $user, $password, $params);

} catch (PDOException $e) {
    echo $e->getMessage();
    exit;
}

$sth = $db->prepare('SELECT * FROM sbtest1 WHERE id =?');
$sth->execute([28]);
$res1 = $sth->fetchAll(PDO::FETCH_ASSOC); 
print_r($res1);
?>

table :

CREATE TABLE `sbtest1` (
  `id` int(10) unsigned NOT NULL,
  `k` int(10) unsigned NOT NULL DEFAULT '0',
  `c` char(120) COLLATE utf8mb4_bin NOT NULL DEFAULT '',
  `pad` char(60) COLLATE utf8mb4_bin NOT NULL DEFAULT '',
  `d` varchar(500) COLLATE utf8mb4_bin NOT NULL DEFAULT 'a',
  PRIMARY KEY (`id`),
  KEY `idx_d` (`d`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin

ddl:

alter table sbtest1 add column daa varchar(2) not null default 'd' after k;

php info:

php-pdo-7.2.31-1.el7.remi.x86_64
php-7.2.31-1.el7.remi.x86_64

php prepare.php：

PHP Warning:  PDOStatement::execute(): MySQL server has gone away in /data/dbadir/20200520/prepare.php on line 21
PHP Warning:  PDOStatement::execute(): Error reading result set's header in 
/data/dbadir/20200520/prepare.php on line 21
Array
(
)

php prepare.php：

PHP Warning:  Packets out of order. Expected 1 received 13. Packet size=5 in 
/data/dbadir/20200520/prepare.php on line 22
Array
(
)

connect proxysql:
PDO::ATTR_EMULATE_PREPARES => false ---> Error
PDO::ATTR_EMULATE_PREPARES => true ---> OK
SELECT * ---> SELECT id,pad,c ---->OK (ATTR_EMULATE_PREPARES=true/false)

connect MySQL:
PDO::ATTR_EMULATE_PREPARES => false ---> OK
PDO::ATTR_EMULATE_PREPARES => true ---> OK
SELECT * ---> SELECT id,pad,c ---->OK (ATTR_EMULATE_PREPARES=true/false)

Why when ATTR_EMULATE_PREPARES is false, does proxysql return an ERROR?