How to avoid memory leaks in frame animation?

Question

I've created simple test app with one activity. The activity contains frame animation. The total size of images in frame animation(riffle_forward_anim) is about 1MB. Here is the code I use to load animation:

public class MainScreen extends Activity {
/** Called when the activity is first created. */

private ImageView imgForward; private ImageView imgBack;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    imgForward = (ImageView) findViewById(R.id.imgForward);

    imgForward.setBackgroundResource(R.anim.riffle_forward_anim);

}

@Override
public void onPause(){
 super.onPause();
 AnimationDrawable anim = (AnimationDrawable) imgForward.getBackground();



 int count = anim.getNumberOfFrames();
 for(int i=0;i<count;i++){
  anim.getFrame(i).setCallback(null);
 }

 imgForward.getBackground().setCallback(null);

 imgForward = null;
}

}

As you can see I try to release memory in onPause() method. Yes, I've read http://developer.android.com/resources/articles/avoiding-memory-leaks.html

Anyway crash occurs if I change protrait/landscape mode several times. I understand that I can handle orientation change and avoid crash but I need to release memory in my other app without orientation change. That is why I've created simple test app to understand how realisng memory works. Can anyone give me a hint on how to implement this?

Thanks