Magento 2.1 Rest API save attribute group does not change attribute_set_id

Question

Preconditions

1. Magento 2.1.7

2. PHP 7.0.18

Steps to reproduce

1. Having a test attribute group:

{
  "attribute_group_id": "103",
  "attribute_group_name": "Test",
  "attribute_set_id": 4,
  "extension_attributes": []
}

2. Send a Rest API request:

PUT /rest/V1/products/attribute-sets/4/groups

Headers:

content-type: application/json
Authorization: Bearer <authorization token>

Body:

{
  "group": {
    "attribute_group_id": "103",
    "attribute_group_name": "Test",
    "attribute_set_id": 13,
    "extension_attributes": []
  }
}

Expected result

{
  "attribute_group_id": "103",
  "attribute_group_name": "Test",
  "attribute_set_id": 13,
  "extension_attributes": []
}

Actual result

{
  "attribute_group_id": "103",
  "attribute_group_name": "Test",
  "attribute_set_id": 4,
  "extension_attributes": []
}

Response 200 OK.

Works if changing "attribute_group_name".

Answer 1

Acknowledged as a bug. Link to the issue on GitHub.