Changing ship to code in sales order

NAV 2013.
In a sales order, i change the ship code to a different country than the sales order had.
And i get a message that tells "If you change ship to code, the existing sales lines will be deleted and new sales lines based on the new information on the header will be created. Do you want to change ship to code?"
This change doesn´t change the "vat bus. posting group" neither "business posting group".
Why NAV needs to delete the sales lines?

Thank you!