Partner Determination in Sales Order

Hi Gurrus,

I have come across a situation where I need your support.

I have a business process that "Ship-to-party" on sales order header should only be from the the ship-to-parties of the selected "Sold-to-party".

Right now I can select any ship-to-party regardless of that he is defined in the Partner list of the Sold-to-party or not.

Please suggest how can I restrict system.

Regards: