Major Issue in Payments checkout & pending orders in admins dash

When a user does not complete the checkout process, the pending orders of this product multiply by checkout attempts in admin/seller.

Please reproduce and tell me, what is going wrong on my site:

1. User puts item in shopping card (a donation in this case)
2. User clicks PayPal to checkout, the PayPal window opens
3. User does NOT login to PP to pay but clicks return to site
4. The Item is still visible in Users ShoppingCart, OK so far

...and now the problems start -->

1. Admin has this order as pending order in /page/payment-orders?type=pending
2. User goes back to his Cart and clicks PayPal again to finish the payment of this order. PP window opens but user does not login to PP again and does not pay for the second time
3. Now admin has this order twice in his pending order page
4. User trys again (the third time), but now with another payment provider, maybe CASH or Points or whatever provider is enabled and does not finish the payment...
5. So admin has now 3 pending orders of the same ITEM - 2x PayPal and 1y Cash
6. to be continued.....

Using 13RC2, Una hosted cloud