This problem has arisen again. This is the response from the client early this morning which I've made private as it contains some customer info (see below).
Would it be possible for you to take a look at the log file to establish what has happened? I cannot comprehend how the order ID's are out of sync.
Looking at the data in the database, there is an order 4045 assigned to customer 3496 (the customer detailed below), however there is also an order 4046 which has a user ID of 0 and a form ref of 0.
Could this be a case of the customer not letting PayPal complete and clicking Back in their browser? Or closing the browser and starting again in a new window? If so, is there anything we can do to stop this happening?