Android AdMob: addView doesn't show ad until return to activity

I had the same issue, all I had to do was bring the adView to the front when it was loaded. (I recommend this over loading it twice)

mAdView.setAdListener(new AdListener()
{
    public void onAdLoaded()
    {
        Log.i("Ads", "onAdLoaded");
        mAdView.bringToFront();
    }
}

I was having the same problem, and setting the AdView's visibility to GONE and then back in onAdLoaded seemed to fix it for me:

adView.setAdListener(new AdListener() {
    @Override
    public void onAdLoaded() {
        int visibility = adView.getVisibility();
        adView.setVisibility(AdView.GONE);
        adView.setVisibility(visibility);
    }
});

Less wasteful than making a duplicate ad request and you don't have to sacrifice your original z order.