Hello guys,
replace your PUT request to this code to fix the bug.

public static UnityWebRequest Put(string uri, byte[] bodyData)
{
return new UnityWebRequest(uri, "PUT", (DownloadHandler) new DownloadHandlerBuffer(), bodyData == null || bodyData.Length == 0? null : (UploadHandler) new UploadHandlerRaw(bodyData));
}

Still happening in 2017.4.8f1. Please fix this

Still happening in 2018.3!

Still happening in 2017.4.1f1

Still happening on 2017.2.1p2 with a UnityWebRequest.Put

Use the following code:

protected virtual IEnumerator PostEmptyBody(string route)
{
var headers = new Dictionary<string, string>
{
{ "Content-Type", "application/json" }
};

var packetToSend = JsonUtility.ToJson(string.Empty);

var body = Encoding.UTF8.GetBytes(packetToSend);

var www = new WWW(route, body, headers);

yield return www;

if (!string.IsNullOrEmpty(www.error))
{
Debug.Log(www.error);
}
}

Cheers,

Still happening on 5.6.1f1