PayPal payments and Guest accounts

Has anyone noticed an unusual number of incomplete PayPal orders, which have actually cleared PayPal? We noticed recently that a number of successfully charged Paypal orders are showing as incomplete on our end, and that most of them are from orders placed on a guest account. Naturally, the customer is wondering why they paid, yet the order shows as incomplete, and tracking them down constantly is getting a bit old. We've had 7 so far this month. Thanks for any input.:)