Magento – Persistent Cart Off, Adding 1 Product and Login Results in 12 Products in Cart

On our cPanel boxes, missing assets were serving the entire Magento page.

cPanel's defaults to ErrorDocument 404 /404.shtml but /404.shtml doesn't exist in Magento's document root, so the .htaccess gets executed again and redirects /404.shtml to index.php (using mod_rewrite).

Magento's default .htaccess should specify 404, 500, and other error handlers explicitly.

To fix this beahviour, we added the following to our .htaccess:

ErrorDocument 404 /errors/404.php

We probably should also add 500s as well:

ErrorDocument 500 /errors/500.php

Use an event observer to empty cart on customer login.

config.xml

<customer_login>
  <observers>
      <foo_bar> <!-- foo_bar should be unique tag for within all customer_login observers-->
          <class>foo_bar/observer</class>
          <method>customerLogin</method>
          <type>singleton</type>
      </foo_bar>
  </observers>
</customer_login>

Observer

class Foo_Bar_Model_Observer {
    public function customerLogin(Varien_Event_Observer $observer) {
        foreach( Mage::getSingleton('checkout/session')->getQuote()->getItemsCollection() as $item ) {
            Mage::getSingleton('checkout/cart')->removeItem( $item->getId() )->save();
        }
    }
}