I can't see a problem with that...Someone mentioned earlier that the image is rotated 180 degrees by the lens, which is why it is upside-down on your ground glass, but correct me if I'm wrong somebody, that amazing feat of physics occurs after the light has passed through the filter on the front of the lens. Logic tells me that everything that occurs in front of the lens will be flipped when it reaches the ground glass, including the polarizing effect. What a strange thing to think about!
Oh, and are you composing with your head under a dark cloth? Keeping things as dark as possible makes it easier to see what is happening on the glass.