loading customize dataset error

We recently trying to test on our customized dataset. By using the D3MDatasetLoader(), it can be loaded successfully, but it turned out the metadata was incorrect.

First if we load the dataset with correct dataset (we use 38_sick as an example here), we should have nothing inside the dataframe's metadata as shown below.

(d3m-devel-201902) ➜  dsbox-ta2 git:(jun_test_v2019) ✗ python
Python 3.6.8 |Anaconda, Inc.| (default, Dec 29 2018, 19:04:46) 
[GCC 4.2.1 Compatible Clang 4.0.1 (tags/RELEASE_401/final)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> import os
>>> from d3m.container.dataset import D3MDatasetLoader, Dataset, CSVLoader
>>> dataset_file_path = '/Users/minazuki/Desktop/studies/master/2018Summer/data/new_small/38_sick/TRAIN/dataset_TRAIN/datasetDoc.json'
>>> # dataset_file_path = '/Users/minazuki/Desktop/studies/master/2018Summer/data/customize/bibtex_dataset/bibtex_dataset/datasetDoc.json'
... loader = D3MDatasetLoader()
>>> dataset_train = loader.load('file://{dataset_doc_path}'.format(dataset_doc_path=os.path.abspath(dataset_file_path)))
>>> dataset_train['learningData'].metadata.pretty_print()
Selector:
 ()
Metadata:
 {}
>>> 

However, when loading our customized dataset, the metadata was wrong as shown below. If we further look inside the metadata, it turns out the metadata was changed to be a pandas.Series object instead of Metadata object.

>>> 
>>> dataset_file_path = '/Users/minazuki/Desktop/studies/master/2018Summer/data/customize/bibtex_dataset/bibtex_dataset/datasetDoc.json'
>>> dataset_train = loader.load('file://{dataset_doc_path}'.format(dataset_doc_path=os.path.abspath(dataset_file_path)))
>>> dataset_train['learningData'].metadata.pretty_print()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/minazuki/miniconda3/envs/d3m-devel-201902/lib/python3.6/site-packages/pandas/core/generic.py", line 4376, in __getattr__
    return object.__getattribute__(self, name)
AttributeError: 'Series' object has no attribute 'pretty_print'
>>> 

It should be something wrong with our customized dataset, but we can't figure out where the error on the dataset and maybe it is a bug inside the D3MDatasetloader that could be fixed.

Here attached is the dataset file. https://gitlab.datadrivendiscovery.org/jliu2/isi-testing-datasets/tree/master/bibtex_dataset