Tween events with problems?

Hello again Kirupa Forum!

I want to ask if anyone else had the same problem… the effects that uses the tween class sometimes go wrong. Heres an example:

[SIZE=2][COLOR=DimGray]import fl.transitions.Tween;
import fl.transitions.easing.*;
import fl.transitions.TweenEvent;

var iTween2:Tween;
iTween2 = new Tween(cartao, “y”, Regular.easeOut, cartao.y, z*calculate_height(main_menu.length), 1, true);[/COLOR][/SIZE]

It works, but sometimes, something around 1 chance in 25, the animation finishes in an undesired position. Someone knows why?