A normal purchase requisition is created, line added and workflow submitted. Then approved.
In the purchase policy, the parameter "Automatically create purchase orders" is marked.
Therefore a purchase order is created.
When you go to this PO, it's automatically approved. But when going to Workflow button, you click there and a button with empty text appears and when you click it shows an error "No object specified on menu item".
The workflow button should be disabled is there is nothing to show.