When using a shader in GH in Rhino Rendered viewport mode the GH geometry displays despite the preview being switched off in GH. In wireframe or normal shaded mode the GH geometry does not display as expected. Please see screenshot below:
This is intended behaviour, the Custom Preview component will either draw previews in non-render-display modes or it will add meshes to the display pipeline in render-like modes. If you don’t want this you have to specifically disable the render meshes on each custom preview component.