Demand Plan / Supply Plan / Sales Order / Special Work Order

Has anyone else encountered this or am I doing something wrong?

We enter Sales orders for Assemblies that we build in-house.
We enter Work Orders to Make to Stock.
For larger Sales Orders we create Special Work Orders (simplifies fulfillment).
When we create a Demand Plan (Forecast and Orders or Forecast Consumption), the open sales orders are included in the demand.
Note: Both sales orders with special work orders and sales orders that will commit from stock (i.e., no special work order) are included as demand.
Unfortunately, the Special Work Orders created are not considered in the Supply plan.