title: Tensorflow Estimator gives different prediction result on each call of predict
body: <p>I trained a classifier for my own dataset using TF Estimators, but after each prediction call I'll get different prediction results. I checked the dataset and the data example order  is alright , same for every prediction call , but the model will give different classification result. I'm so confused , wonder if I'm making something wrong.</p>
  
  <p>This is my code for reading input:</p>
  
  <pre><code>    def parse_predict_record(example):
          features = {"user_id": tf.FixedLenFeature([], tf.int64),"ad_info": tf.VarLenFeature(tf.string)}
          data = tf.parse_single_example(example, features)
          uid = data['user_id']
          ad_info = tf.sparse_tensor_to_dense(data['ad_info'], default_value='0')
          test_info = tf.sparse_tensor_to_dense(tf.string_split(ad_info, "#"), default_value="0")
          test_info = tf.string_to_number(test_info, out_type=tf.int32)
  
          feature_dict = {"user_id": uid, "ad_info": test_info}
          print("feature_dict=", feature_dict)
          return feature_dict
  
      files, cnt = get_files(FLAGS.predict_path)
      predict_dataset = tf.data.TFRecordDataset(files).map(lambda x: parse_predict_record(x)) \
          .padded_batch(FLAGS.batch_size, padded_shapes={'user_id': [], 'ad_info': [None, None]}) \
          .prefetch(32)
      iterator = predict_dataset.make_one_shot_iterator()
      return iterator.get_next()
  </code></pre>
  
  <p>code for prediction:</p>
  
  <pre><code>        print("start predict")
          result = model.predict(input_fn=predict_input_fn,
                                 hooks=[tf.train.LoggingTensorHook([ 'user_id', 'ad_info', 'predict_id'], every_n_iter=500)])
          prediction_res = []
          for prediction in result:
              # print("predictions=", prediction)
              user_id = prediction['user_id']
              predict_label = prediction['predict_label']
              print("usre_id=", user_id)
              print("predict_label=", predict_label)
  
  </code></pre>