This has happened to me too.  Buyer purchased item yesterday and supposedly paid via Paypal. Item shows payment pending.  I checked my account and no funds or any notification of pending payment there.

Have now rung Paypal and they told me to check the address in the listing.  Lo and behold the address showing does not exist!!!  It is a mutation of an my old email address and my new email address (change last month).

How to fix?  Paypal tell me to contact buyer and ask them to cancel payment, and resend to correct address. I have contacted Buyer and send another invoice which shows my correct Paypal address but haven't heard back yet.

I have since checked all 84 listings and found another listing with the same error.  Have now done a bulk edit to make sure all Paypal addresses in my listings are correct.  Paypal don't tell me how this has happened, is this a maintenance glitch?