In Zen Cart v1.3.9d (and probably previous) when updating the quantity of a product from the shopping cart page the following error appears twice in the myDebug log:
I believe this is being caused by a line in /includes/classes/shopping_cart.php in function actionUpdateProduct() at about line 1543:
PHP Warning: explode() expects parameter 2 to be string, array given in /home/glitterm/public_html/includes/functions/functions_general.php on line 566
...I think it should read...
$cart_qty = $this->in_cart_mixed($_POST['products_id']);
$cart_qty = $this->in_cart_mixed($_POST['products_id'][$i]);