PO Document Style to be created with Only one Document Type : Blanket PO

Dear All,

Client needs to create New Document Style that will be linked to Blanket PO Doc Type only so that they can segregate Blanket PO according to the respective Style.

Now When i go to define document Style. There is a region For Document Type and following is displayed.

Type

Standard Purchase Order

Contract Purchase Order

Blanket Purchase Order

After defining Document Style name, I select Blanket PO and i Put Display name as per client requirement.

But I can see that Standard Purchase Order Document Type remains enabled and i can not disable it and system is not allowing me to save new document type since i did not provided display name for Std PO Document Type.