Moving Faces

I am new to the 3D features of Autocad 2000. I have come across a
specific issue that I would like help with.
I have created a .5" thick solid plate. In the plate I placed several
counter-sunk through-holes. I did that by creating a solid
representation of the holes and subtracting the shape from the solid
plate. Later, I realized that I needed more holes of the same size on
the plate. I used the SOLID EDITING>COPY FACES command to add holes to
the plate. Everything appears fine in the 3D WIREFRAME view, but when I
view the model in the FLAT SHADED view, the new holes are "filled". The
faces of the holes are there, but I cannot "see through" the holes in
the FLAT SHADED views.
Is there a way to use the COPY FACES command so that the material inside
of the holes is removed during the copy procedure? If not, is there
another command that will easily remove the solid material from inside
of the holes since the faces of the holes are already there? I am trying
to avoid having to go back and re-create the solid model for the holes
and do another subtract when this happens in the future.
Thanks for any help that you can provide.