DuplicateMC question!

ok, I want to make a game were coins fall from top and I need them to be duplicated. However, I can’t make a copy of it without having the original deleted. Whenever my coin reaches certain point of the movie, I want another to fall but without the first one dissappearing. Here is the code I’m using:

In the main timeline:

dupMovie = function () {
 i= i + 1;
 circle.duplicateMovieClip("circle"+i, i, {_x:Math.random()*300});
} 

In the coin mc inside the main mc:

 
onClipEvent(enterFrame){
 _y +=6;
 if(_root.circle, hitTest(_root.barrera)){
  _root.dupMovie();
 }
}

It duplicates but eliminating the one before… what’s the problem?