GridFs file is stored incorrectly after two flushes

/** @Document(db="tests", collection="fs") */
class File
{
    /** @Id */
    protected $id;

    /** @File */
    protected $file;

    function  __construct($source) {$this->file = $source;}
}

$file = new File(__DIR__ . '/test.txt');

$dm->persist($file);
$dm->flush();
$dm->flush();

{
  "_id": "4c777fc00f9d505407020000",
  "filename": "/test.txt",
  "uploadDate": {
    "sec": 1282899904,
    "usec": 0
  },
  "length": 10,
  "chunkSize": 262144,
  "md5": "76ce9f441de2ed5de337d391ad4516b7"
}

{
  "_id": "4c777f780f9d508416020000",
  "chunkSize": 262144,
  "file": {
    "file": {
      "_id": {},
      "filename": "/test.txt",
      "uploadDate": {
        "sec": 1282899832,
        "usec": 0
      },
      "length": 10,
      "chunkSize": 262144,
      "md5": "76ce9f441de2ed5de337d391ad4516b7"
    },
    "": {
      "w": 1,
      "wtimeout": 10000,
      "chunks": {
        "w": 1,
        "wtimeout": 10000
      },
      "": "fs.chunks"
    }
  },
  "filename": "/test.txt",
  "length": 10,
  "md5": "76ce9f441de2ed5de337d391ad4516b7",
  "uploadDate": {
    "sec": 1282899832,
    "usec": 0
  }
}