title: Paypal Web Payment Pro hangs when order is submitted
body: <p>Sometime last weekend our Opencart install, version 1.5.1.3 started to process duplicate orders for CC payments made through PayPal Website Payment Pro. It happens in the same order sometimes it will process twice. Sometimes 3 times.Payments made through Paypal Web Standard module is working fine. </p>
  
  <p>I looked in the erros logs and about the same time this started happening, we started to get these php notices.</p>
  
  <p>2013-04-23 3:44:01 - PHP Notice: Undefined index: customer_id in /var/www/vhosts/xxxxxxxxx.com/httpdocs/system/library/customer.php(170) : eval()'d code on line 4
  2013-04-23 3:44:01 - PHP Notice: Undefined index: payment_address_id in /var/www/vhosts/xxxxxxxxx.com/httpdocs/system/library/customer.php(170) : eval()'d code on line 4</p>
  
  <p>I don't know if they are related, but they started to crop up right at the same time. I went way back in the logs and did not see these anywhere else. Strange for this to pop up out of the blue the cart has been working fine, up until now. </p>
  
  <p>I did a request of new API credentials from PayPal and reinstalled the web payments pro module in Opencart. This seemed to help initially, but we still had orders yesterday that came in as duplicate in the same order. We got a bit of feedback from some customers and it seems that that people are getting hung up on the "please wait..." part when they submit their order. We would get this initially from time to time, but all of a sudden it is much more frequent. The page submits the order, but then never returns the success page. Keeping customers from pressing the button again would help, so we put up a script that blocks the user from pressing the submit order button again. </p>
  
  <p>Unfortunately it still doesn't solve the source of the issue, in that the communication between the site and the payment processor is getting hung up somewhere. I'm guessing paypal made some changes on their end to cause this issue, but any suggestions where I could look to get this corrected would be much appreciated. Thanks. </p>