I created a GUI Viewport now and render a ball / character into it right now, what should I do so the environment should not effect on this? As you can see, if you move the camera to the ground when the character will end up in the Viewport ball / char.

Here is a picture on my problem, I want it to look like pic4 all the time.

I guess you have something wrong with the codes, on first look it seems like the z buffer isn't cleared.
what code do you have in rendering/drawing of the viewport?

it is suggested to use Renderer with combine (just like in the tut of combining)
if you don't want to use Renderer, try clearing the zbuffer before rendering with D.clearZ

Thanks, D.clearZ did the trick fore render.