[FIX] account: set fiscal position on customer invoice in the same fashion as on SO

addons/account/models/account_invoice.py

@@ -480,7 +480,9 @@ class AccountInvoice(models.Model):
             else:
                 account_id = pay_account.id
                 payment_term_id = p.property_supplier_payment_term_id.id
-            fiscal_position = p.property_account_position_id.id
+            addr = self.partner_id.address_get(['delivery'])
+            fiscal_position = self.env['account.fiscal.position'].get_fiscal_position(self.partner_id.id, delivery_id=addr['delivery'])
+
             bank_id = p.bank_ids and p.bank_ids.ids[0] or False
 
             # If partner has no warning, check its company