In specular reflection result depends on view vector from camera to point. Because of that, when doing temporal reprojection and reprojecting position of current fragment while camera is translating, result color is changing and it induces ghosting. To mitigate this, motion is detected to dampen temporal reuse when moving. In diffuse there is no such dependance and this problem doesn't exists.
Is there a method to calculate aproximate position of current frame specular color (if it exists) in previous frame to produce a coherent results?