I've finally found out the reason why banner was overplayed by game scene. The mistake is actually silly.
following methods must be updated:
@Override
public void onPause() {
**if (adView != null) adView.pause();**
super.onPause();
CCDirector.sharedDirector().pause();
}
@Override
public void onResume() {
super.onResume();
CCDirector.sharedDirector().resume();
**if (adView != null) adView.resume();**
}