CakePHP虚拟字段发送报头

我有一个Users表，其中包含以下数据:

class User extends Entity
{
protected $_virtual = ['createdformated','modifiedformated'];
protected function _getCreatedformated()
{
    $date = new Time($this->_properties['created']);
    $final=strftime("%d/%m/%Y %H:%M", $date->getTimestamp());
    return $final;
}
protected function _getModifiedformated()
{
    $date = new Time($this->_properties['modified']);
    $final=strftime("%d/%m/%Y %H:%M", $date->getTimestamp());
    return $final;
}
}

如果在我的控制器中我调用:

    $logusers["data"] = $this->Logusers->find('all')
       ->contain(['Users'])
       ->order(['Logusers.id'=>'DESC']);
     echo json_encode($logusers);

在jsonenconde

 Warning (512): Unable to emit headers. Headers sent in file=C:'wamp'www'otras'mailing'src'Controller'UsersController.php line=91 [CORE'src'Http'ResponseEmitter.php, line 48]

如果我只留下1(ONE)个虚拟字段，问题就解决了…只有当我同时启用它们时才会出现问题。

有什么问题吗?