About Costumers in Transaction

Hello, I am using aronium recently and this program's really great. But I have a bit of problem. After I imported the costumers list and then tried to make a transaction with one costumers as trial (say the costumers is named as A). After that, I make a few transactions but I didn't choose the costumer choice in the payment pages, as far as I know, the transaction will have "unknown" as costumer if I don't choose the costumer at payment page). But when I check the documents of transaction which I didn't choose the costumers, all of them was set to A rather than set to unknown. Have I set something wrong?