Shop creates two orders

[bacuri]

I've have shop (presta 1.6) that uses modified paypal module (which adds paypall fee). Sometimes when client pays with paypal shop creates two orders instead of one. One order has all products and the other one order has one position with paypal fee. It happened few times.

When it happened in database in orders table there are two records. They have different order numbers and different id_carrier. This is strange, how can be to different shipping methods if in cart there is one method selected? Can anybody tell me how it is possible? 

In this topic 

innovacy wrote:

Quote

This is a behaviour as expected... Another reason can be different warehouses and/or carriers

so it looks it is possible, but when does it occurs and why?