I resetted my miix today so i was able to figure out if the miracast has really differences in function without all the updates. O can confirm it is like that. With stock OS thwre is duplicate screen working. What i found out is that with stock OS it is in portrait mode and shows the screen in landscape so half of the screen is used on the lenovo and full screen on the miracast device which is not optimal. I decided right now to install all updates from microsoft again an stay with the fucked options which only can access extended screen. This is really poor so o have to wait for optimized drivers from lenovo.