"IExtendedProperties" on payment disappear after saving cart as a purchaseOrder

Hi Forum,

I have a question about "IExtendedProperties". After saving a cart as a purchaseOrder, the values added to "IExtendedProperties" on payments disappear.

Is it a bug or intended behavior. Do I misunderstand something? :)

Screenshot cart order form
https://screenpresso.com/=j1wlf

Screenshot purchaseOrder order form
https://screenpresso.com/=DZgdc

Code

var orderReference = _orderRepository.SaveAsPurchaseOrder(cart);
var purchaseOrder = _orderRepository.Load<IPurchaseOrder>(orderReference.OrderGroupId);

EpiServer.Business.Commerce
12.17.2.3575

BR
Lasse