Unity Ads keep playing after closing a ad?

Hi

I added the script from "Getting started it's that simple" from the unity asset store plugin.

using UnityEngine.Advertisements;
using UnityEngine;
using System.Collections;

public class Ad2 : MonoBehaviour {

// Use this for initialization
void Start () {Advertisement.Initialize ("ID#");

}

// Update is called once per frame
void Update () {if(Advertisement.isReady()){ Advertisement.Show(); }

}
}

When I press the ad close button the ads keep playing one...

Unity Ads keep playing after closing a ad?