[JAVA] Generates String instead of OffsetDateTime

Description

A reference in an object in the definitions part to a primitive date-time is generated as String instead of OffsetDateTime.
I tried this with the definition on my local machine with swagger-codegen-cli but I get the same result when generating a java client on editor.swagger.io
The generated class io.swagger.client.model.Test has 2 fields, date1 of type OffsetDateTime and date2 of Type String.
I would expect both fields to be of type OffsetDateTime.
Here is an excerpt from the code:
@javax.annotation.Generated(value = "io.swagger.codegen.languages.JavaClientCodegen", date = "2019-08-14T07:51:15.087Z")
public class Test {
@SerializedName("date1")
private OffsetDateTime date1 = null;

@SerializedName("date2")
private String date2 = null;

Swagger-codegen version

2.3.0 and 2.4.7 (and probably more)

Swagger declaration file content or url

swagger: "2.0"
info:
title: "Test"
version: "2"
paths:
/test:
get:
produces:
- "application/json"
responses:
200:
description: "success"
schema:
$ref: "#/definitions/Test"
definitions:
Date:
type: "string"
format: "date-time"
Test:
type: "object"
properties:
date1:
type: "string"
format: "date-time"
date2:
$ref: '#/definitions/Date'

Steps to reproduce

Insert swagger definition in editor.swagger.io and generate java client.

Use the supplied Swagger 2.0 definition as the reproduction input, generate the Java client, and compare inline date1 with referenced date2 in io.swagger.client.model.Test. Trace the Java client generation path for referenced primitive date-time schemas; done when both fields are OffsetDateTime and the generated output matches the expectation.