Coplanar polygons are not joined

[oschakravarthi]

Hi,
Assume that I have a Polygon which is nothing but a rectangle.
I have another Polygon which is also a rectangle and I am subtracting it from the 1st polygon.
(Like subtracting a window from a wall). Both polygons are co-planar.
For simplicity, lets forget about the 3rd dimension

I expect a polygon with 8 points but I am getting 4 polygons.

1. The rectangle above the window.
2. The rectangle right side of the window
3. The rectangle left side of the window
4. The rectangle below the window.

As all these Polygons are co-planar and connected, I expect a single polygon.

Is it a bug? or Is there a way to join them?

Thanks