wait,have you downloaded the blender version with the old compiler?i dont know if this could be the same bug behavior,but in this developer thread, the new AO shader shows strange results, with the old compiler blender version.with the new compiled version the bug was not there.
maybe you should link your thread there,maybe its a bug.
edit,in the link you are posted seems the same bug behavior,maybe the bug is not fixed yet,so the best would be you report it,otherwise its got no fix if no dev knows it.