board geometry

Using 17.2

I created my board outline using class/subclass 'Board Geometry/Outline'.  When i create artwork is tells me that the preferred sub class is 'Design_Outline'.  How do i change the subclass?  If i select the outline, and use change class/subclass, 'Design_Outline' is not listed.  Both 'design_outline' and 'outline' appear in the color dialog under 'Geometry'

Thanks