A diagram is always opened without stencil. Even if you open the stencil for the diagram, save the diagram, than close it and open again, the stencil is always lost. This problem appears not only in process4.biz, but also if you open the diagram in Visio only.
Open the Drawing Explorer Window from the Visio Developer ribbon.
Open property of the diagram in the Drawing Explorer. Under the tab Summary activate the checkbox Save workspace.