Cycles Rendering: Black texture casts a shadow on object.

Blender : 2.68a, 2.69
Reder Engine: Cycles
OS : Win7 x64

I added a Texture to an object.
This Texture is a withe image with a black “13”, a black font and a green stripe on it.
On the left side of my picture you see the correct render result.

For speed up i tried to use post compositing, to get a better result in less time.
So i knew that the shadow layer is one of my most noise layers.

But if i look in the shadow layer, there is the black “13” of my texture. (See the right side of my image)
But that should not happen.

Could some one tell me how to stop that?

And why is only the black casting shadows?
If all Texture casts shadows, there should also be a light dark stripe.

And i think it is wrong. Because my texture shouldn’t cast shadows on the own object.
If i try to blure the shadows, it will blure the hole render result around the “13”.
Without that shadow of the “13”, i could blure the shadow layer without any problems for the render result.
OK, i could not have sharp shadows, but that is not needed for my rendering.

Could i stop my textures from casting shadows?

best regards

I tested it. Only real black is casting a shadow.
I did a workaround and added a “RGB Curve” to my texture.
It only puts the light point of “x:0,y:0” to “x:0,y:0.01”.

so there is no real black anymore and the bug is gone.

It also works with “x:0, y:0.0001”.