It will be a better idea to download from the zen site the script, Paypal Sessions Order. With that you will be able to track all your paypal transactions. I had that issue befor and still could not sort it out.

The link to download: <A HREF=http://www.zen-cart.com/index.php?main_page=product_contrib_info&cPath=40_41&products_id=84>Paypal Session Viewer</A>