Web Accept PayPal Receipt?

Hullo, all!

I think two-three times this year I received a weird Payment Notification email from PayPal when someone places an order, with no certain reason.
The payment goes through just fine, every penny but the item description is not there as usual.

The Notification of Payment from PayPal looks like this:

Description ------------------ Unit price ----- Qty ------- Amount

My Store Name---------------$10.00-----------1----------$10.00
Purchase
Item# Store Receipt

                                                   Subtotal    $10.00 USD
                                                        Total    $10.00 USD
                                                  Payment    $10.00 USD 

The transaction in PayPal looks something like this. Note "We have no shipping address on file" and the "Web Accept Payment Received" as opposed to the usual "Express Checkout Payment Received"):

---------------------------------------------------
We have no shipping address on file.

Web Accept Payment Received (Unique Transaction ID #12345678910111213)


Name: 	
	Joe Doe    (The sender of this payment is Verified)
Email: 	
	[email protected]
Payment Sent to:
  	
	[email protected]

Total Amount: 	
	$10.00 USD
Fee amount: 	
	-$0.39 USD
Net amount: 	
	$9.61 USD


	Issue a refund Help
  	
	You have up to 60 days to refund the payment.

Item amount: 	
	$10.00 USD
Sales Tax: 	
	$0.00 USD
Shipping: 	
	$0.00 USD
Handling: 	
	$0.00 USD
Quantity: 	
	1

Item Title: 	
	My Store Name Purchase
Item Number: 	
	Store Receipt
Custom: 	
	zenid=SomeRandomNumberHere.
Date: 	
	Jan 19, 2011
Time: 	
	15:19:04 PST
Status: 	
	Completed  

Payment Type: 	
	Instant
------------------------------------------

The transaction looks fine in Zen Cart's order list.

Again, this is sporadic and I can't figure out why.
Any clues will help!

Thanks,
Gabstero.