Multiple orders using same cookie, order number paypal rejects

Wondering if anyone else has experienced this issue with their orders…

[font=arial, sans-serif][size=1]customer places order; completed the order with PayPal and was returned to the site. [/size][/font]

[font=arial, sans-serif][size=1]customer CLOSED their browser (to ensure that the cache was cleared); then re-opened their browser and ATTEMPTED to place another order, but when the order went to PayPal it indicated the invoice had already been paid and would not let them place a new order. [/size][/font]

[font=arial, sans-serif][size=1]customer again CLOSED their browser, re-started their computer and ATTEMPTED to place the order again with the exact same result when trying to complete the payment with PayPal.[/size][/font]

[font=arial, sans-serif][size=1]On my side, the order number reflected the order they tried to place; but paypal showed that same order number with their original purchase. My email notification indicate the correct first order.[/size][/font]

[font=arial, sans-serif][size=1]The customer refuses to clear cookie cache in browser. [/size][/font]

[font=arial, sans-serif][size=1]Any ideas what may have happened here? (fist time this has ever happened)[/size][/font]