PDFView drawPagePost: does nothing

I am trying to subclass a PDFView overriding -drawPagePost: to add some custom highlights.. However, none of my drawing is visible on the drawn page. In the overridden method I have transformed the current graphics context to go to page space using -transformContextForBox: (though this makes no difference). Does anyone know what's going on, and has anyone ever succeeded in drawing using this method?

thanks,
Christiaan