DrByte:
Yes: Use PayPal Express Checkout instead.
We just had this happen on our site today using PayPal Express.
This was a PP Express Checkout order because there was no new customer registration for this person and PayPal shows 'Express Checkout Payment Received'.
Nothing is showing in the PP debug file.
All we got were two PP emails for two separate transactions within minutes of each other (different transaction ids), but each one for the same identical item.
We offer free shipping for orders over $99. The PP payment email we received had a model # attached to it and was for an item priced at $119.95, but shipping had been charged.
I know occasionally I've seen a 'lag' in PP orders showing up in the admin, but we got these emails over 3 hours ago and nothing is showing in the admin.
The customer did contact us a few minutes ago asking to cancel one of the duplicate orders. We have contacted him back and are awaiting his reply to see what/if anything he experienced on his end.
Any ideas what might be going on?
Edited to add: 1.3.9h version cart
Only payment mods installed/in use are Authorize.net, PayPal Website Payments Pro and PayPal Express.
I'll finish that project tomorrow, I've made enough mistakes today!