This script shows the behaviour: 

<?

class Cart {
        var $items;             /* array de articulos */

        function Cart() {
        /* object constructor */
                $this->init();
        }

        function init() {
        /* inicializa y resetea la cesta */
                $this->items = array();
        }

        function add($productid, $qty) {
        /* aM-qade un articulo a la cesta aM-qadiendo el numero de unidades*/
                if (isset($productid)) {
                        if (! isset($this->items[$productid])) {
                                $this->items[$productid]=0;
                        }
                        $this->items[$productid] += $qty;
                }
        }

}

session_start();
session_register("SESSION");

if (! isset($SESSION)) {
        $SESSION = array();
}

if (! isset($SESSION["cesta"])) {       // This is supposed to be executed
        echo "INITIALIZING CART<BR>\n"; // just 1 time in the session,
        $SESSION["cesta"] = new Cart;   // isn't it?
}


$SESSION["cesta"]->add('cameras',1);    // Add 1 to the 'cameras' item

echo "Cameras: ";
echo $SESSION["cesta"]->items['cameras'];
echo "\n";

?>

When executed with PHP 4.0.2 it increments the counter for the 'cameras' item in the items array of the 'cesta' object.

when executed with PHP 4.0.3 (or 4.0.3pl1), it always resets the counter and prints the "Initializing object" message.

Thanks for your help, and congratulations for your work...

BTW, any1 going to ApacheCON next week?

Fixed in CVS.