Note that when adding an sprite to a container (sprite or movie), only the object added to the sprite before the addin to the container will be displayed.
<?php
// In this case, myShape will be displayed...
$sp=new SWFSprite();
$container=new SWFSprite();
$sp->add($myShape);
$container->add($sp);
// but not in this case
$sp=new SWFSprite();
$container=new SWFSprite();
$container->add($sp);
$sp->add($myShape);
?>