title: Why would Magento fail to save a customer after generating an ID?
body: <p>I'm attempting to track down the cause of a rare bug (love those intermittent bugs) where a customer selects to Register at time of checkout, but when the order is completed, Magento somehow fails to save the customer record.  This results in an orphan order with no email address, a difficult customer service situation.  </p>
  
  <p>Here are the results of my investigations so far: </p>
  
  <ul>
  <li>The Sales Order View in adminhtml reports that the customer is a Guest and the email address is blank.  Billing and Shipping addresses are visible.</li>
  <li><code>customer_is_guest</code> is false in <code>sales_flat_order</code></li>
  <li>The <code>sales_flat_order</code> entry links to a valid record in <code>sales_flat_order_address</code>. </li>
  <li>The <code>sales_flat_order_address</code> record contains values for <code>customer_id</code> and <code>customer_address_id</code> however those linked records do not exist.</li>
  <li>There is no discernible pattern in customer information, products ordered, payment methods.</li>
  <li>There are no relevant entries in system.log, exception.log, apache error logs, var/reports or any other logs that I'm aware of.</li>
  </ul>
  
  <p>Thoughts:   </p>
  
  <ul>
  <li>the customer save is progressing far enough that an ID is generated. </li>
  <li>there is an observer on customer_save_after that is causing a rollback of the save?</li>
  <li>a low-level database error is causing the save to fail.</li>
  </ul>
  
  <p>Does anyone have any suggestions on how to track this down?</p>
  
  <p>Version is Enterprise 1.9.</p>