Products not added to quote for certain customers

I’m adding products to quotes with an ajax call to this function

public function addProductAction(){         $  id = (int)$  this->getRequest()->getParam('id');         $  result = Array();         if($  id){             try {                 $  product = Mage::getModel('catalog/product')->load($  id);                 $  quote = Mage::getSingleton('checkout/session')->getQuote();                 $  options = array(                     'options' => array(                         'label' => 'TestOption',                         'value' => 'Test Value',                    )                 );                 $  quoteItem = $  quote->addProduct($  product, 1);                 $  quoteItem->addOption(new Varien_Object(                     array(                         'product' => $  quoteItem->getProduct(),                         'code' => 'additional_options',                         'value' => serialize($  options)                     )                 ));                 $  quote->collectTotals()->save();                 $  result['itemId'] = $  quoteItem->getId();                  $  result['success'] = 1;                 $  result['message'] = $  this->__('Item was added successfully.');             } catch (Exception $  e) {                 $  result['success'] = 0;                 $  result['error'] = $  e->getMessage();             }          }          $  this->getResponse()->setHeader('Content-type', 'application/json');         $  this->getResponse()->setBody(Mage::helper('core')->jsonEncode($  result));     } 

Most of the time the product is added just fine, lately though I’ve been getting good responses from the function but the product does not show up in the cart.

This happened to a customer that I sent a previous call all the way through the checkout process.

I’m getting no errors anywhere inside log or report, and nothing on screen. The function is returning with a incremented sequence of ID’s like you’d expect. It just doesn’t show when you go the the cart page.

Is there something off about this function?