I have not had any luck.

I did just observe a customer that was logged in with 2 different Session IDs.

One Session ID had one item in the cart.

The second Session ID had 2 items (one of the items was the same as in the first Session ID)

I observed all of this on the Who's Online page in real time by chance.

It looks like they are getting to the checkout confirmation page (where paypal drops you back off or where the credit card information is entered (heartland plugin).

Then they circle back through the site and that create some kind of loop and they end up with another Session ID. Another Session ID meaning a second instance of the same customer with a different Session ID.

This one particular customer circled back to add an item.

I can't recreate this but the pattern is that any duplicate orders have all landed on the Checkout Confirmation and then started shopping again or they go into their address information.

The customer I observed never checked out so I don't have 2 invoices but I believe what I observed would have resulted in at least 2 submitted orders. They bailed out of the cart for whatever reason, but not during the checkout process.