Unity3d Coroutine continue failure

unity3d 5.5.2f1 存在

IEnumerator coroutine;

coroutine = DownLoadTextureAsync(url);

 

public IEnumerator DownLoadTextureAsync(string url)
    {
        WWW www = new WWW(url);
        yield return www;

if (www.error == null)
        {           
            m_Texture2D = www.texture;

      }

}

void main()

{

coroutine = DownLoadTextureAsync("url")

StartCoroutine(coroutine);

StopCoroutine(coroutine);//这个unity3d会报错Coroutine continue failure，unity3dBUG

}