Recently I played around a bit with my Sirocco's camera and noticed that the 2x zoom is a bit inconsistent.
When turning on the zoom, it can happen that the camera app is using only digital zoom, instead of the optical zoom from the second camera.
You can check that easily by covering one of the lenses with your fingers.
My impression so far is that the app will favor digital zoom when it considers the light conditions too "bad" for optical zoom - maybe because the aperture of the zoom lens is a bit smaller (higher f Number).
Anyway, one might want to keep that in mind when shooting with zoom - the resolution of the resulting picture can vary noticeably.