Dear milstan,
Solid operations only work for the 3D window. It would not be easy to implement it in 2D, since it can't be exactly defined what the 2D symbol should look like. Floorplan is basically a section of the model, but the height of the section is not the same all over the plan -you want to cut the windows with very different sill heights, for example.
Save the solid operated bodies as an object, and then you can create a 2D symbol of your taste.
HTH,
Greg
Gergely Kmethy
VP, Customer Success, Graphisoft