2 invoices generated for order. Order is canceled before payment

Question

I have following problem:

We are running webshop and sometimes it happens that 2 invoices are generated for 1 order.

Moreover sometimes order gets canceled before even customer goes to payment-gateway.

I'v united those 2 questions, because I think they have some similar reason and perhaps some similar solution.

Our magento version is 1.5.1.0.

Answer 1

@Dez, yeah the timeout thing could do the thing. But unfortunately our gateway doesn't have one.

The problem I had was that Payment gateway generated 2 responses:

1. automatic, when user payed.
2. automatic, when user pressed back button.

So if magento was slow enough to not handle fast first response, the second one will generate second invoice.