I solved the issues with the help of Jane. Has anyone problems as well?

I am redesigning the shader pipeline at the moment to get normal data involved in the postprocessing, too. This way I can use another blurring which shall avoid bleeding. Second, and that is my primary goal, I am working on that the AO is calculated on the half of the screen size. I found an interesting technique for edge preserving upsampling which takes the depth and the normals into account before and after downsampling.