Doccano: Metadata Fields not Populated on Export

System information

• Windows 10, running latest (pulled on 06/17/2019) Docker image
• Python version: n/a, using docker version

Describe the problem

The documentation states:

Any other columns (for csv) or keys (for json) are preserved and will be exported in the metadata column or key as is.

But this is not the behavior I am experiencing. I am using the Docker image version of Doccano running on a Windows 10 host. For a sequence labeling project, I import data in this JSON lines format:

{"external_id": "abc12345", "other_field": 5, "text": "hello world"}
{"external_id": "abc12346", "other_field": 2, "text": "this is a test"}

After labeling the data, I go to _Edit Data_ > _Export Data_ and export in either the _JSONL_ or _JSON(Text-Labels)_ formats (issue appears either way). Here is the output I get with the _JSON (Text-Labels)_ output:

{"id": 101, "text": "hello world", "meta": {}, "labels": [[0, 6, "Something"]]}
{"id": 102, "text": "this is a test", "meta": {}, "labels": []}

There is no "metadata" field as described in the documentation, and the "meta" field does not contain any of my metadata required to join the annotated examples back to the other relevant data required for my use case.

Source code / logs

n/a