Kohana ORM find_all pk(）函数在PHP 5.6.21中返回NULL

我有以下代码，多年来它一直运行良好，但自从我升级到PHP 5.6.21后，它返回NULL。

$model = new Model_Status ();
$results = $model->find_all ();
foreach ( $results as $result ) {
   echo $result->pk ();
}

当我在运行PHP 5.6.20的服务器上回显$result时，mysql中的行数据加载在$_original_values中，$_primary_key_value和$_changed为空，但在PHP 5.6.21中，$.primary_key_value、$_origina _values为空，_changed具有DB列的值

echo Debug::vars($result)
//php 5.6.20
    protected _object => array(6) (
            "id" => string(1) "1"
            "name" => string(4) "Live"
            "code" => string(3) "401"
            "message" => string(12) "site is live"
            "created" => NULL
            "modified" => NULL
        )
        protected _changed => array(0) 
        protected _original_values => array(6) (
            "id" => string(1) "1"
            "name" => string(4) "Live"
            "code" => string(3) "401"
            "message" => string(12) "site is live"
            "created" => NULL
            "modified" => NULL
        )
//php 5.6.21
    protected _object => array(6) (
            "id" => string(1) "1"
            "name" => string(4) "Live"
            "code" => string(3) "401"
            "message" => string(12) "site is live"
            "created" => NULL
            "modified" => NULL
        )
        protected _changed =>  array(4) (
            "id" => string(2) "id"
            "name" => string(4) "name"
            "code" => string(2) "code"
            "message" => string(7) "message"
        )
        protected _original_values => array(0)