Source type in Planning Worksheet

I want to use the Planning Worksheet to create production orders based on Sales order demand.

When I do this, the production order has the Source type as Item.

How do I make this default to Sales Header and contain the sales Order number in the Source No. field ?

I am using NAV 2013 and I have the items set to "Tracking & Action Msg".

Summary:

I create a Sales Order, then use the Planning Worksheet which creates a Planned Production Order.

The Source type in the Production Order is Item

I want it to be Sales Header and have the Sales Order Number showing.

Is there a bug in NAV ? or do I need to change a setting (if so, what setting?)?

Thanks

Dave K