Canceled invoices

From time to time I have to create a cancelation receipt that cancels the previously issued bill. This looks the same as the original, but it has negative amount values. However on importing such receipts it is recognised as an income as AI ignores the minus before the value. So Im forced to import these cancelation receipts as expense. Please train or make an easy option to import these kind of “negative value” documents so they can be properly recognised and stored. TY