Asset Accounting class on a child

 When entering a child against a parent asset if you enter an accounting cost code other than the parents code, it will allow you to enter a different cost code but it will change when you save it but the major accounting class will remain the same. Is this because of processing options for P1201 -  3rd one which should be changed to “Blank”? I tried that and it worked fine. However, I am not too sure why is it defaulted to “1”. Is there a business logic behind it?

Thank you.