Is there a way to fix this issue or at least if you can point me to the correct direction to fix it :
In a shader, discard the pixels like
clip(coord.x > 0.5 || coord.y > 0.5 ? -1 : 1);
Using RenderTargetRGB32F, it generates garbage as it's not clearing it up.
Using RenderTargetRGBA64F, it keeps the image in the buffer and does not clean it.
My expected behaviour was black, it shows me garbage from the RenderTargetR16F buffer.
I know it's an odd thing to try but I was testing something.
Thank you
EDIT : Solved, check Kitsune's method.