API ver. 2025-10 - create_column mutation - board_relation column type does not connect to the target board ID.

I am using the 2025-10 API version, attempting to create a new connected board column. 

The issue I am having is that the target board is not being connected when I provide a JSON string instead of an object. 

The mutation is (board IDs have been changed):

mutation CreateBoardRelation {
  create_column (
    board_id: 1234567890,
    title: "Group",
    column_type: board_relation,
    defaults: "{\"boardId\":0987654321,\"allowMultipleItems\":false,\"allowCreateReflectionColumn\":true}"
  ) {
    id
    title
    __typename
  }
}

If the defaults are provided as an object, it works as expected. There are no parsing errors in the response.