After planned purchase orders are firmed, the ‘Approval status’ is default to ‘Approved’ on purchase order screen, which is skipping the purchase order workflow. Suggest to default the ‘Approval status’ to ‘Draft’ while workflow is enabled; or have a parameter like 'require workflow' to control planned purchase orders. Then the workflow process should work the same way as any other manually created purchase orders.

The reason is: the 'approve' and 'firm' on the planned order screen is normally used by the planning / purchasing department, then workflow is still required from purchase authorisation / financial point of view.