I've seen plenty of dialogue boxes in Android where the keyboard pops up and covers the submit button - and Android doesn't have the button to get rid of the keyboard that iOS has on the bottom right, so it's a bugger to fill in the form and submit it sometimes. So it's not like this problem is unique.
Or those fucking annoying websites with floating banners that slide down, and then when your keyboard pops up, you're left with precisely one line in which to see the text you're entering. Often a line that's about 3 words long. Mobile UIs are still a bit of a mess, even with bigger screens.
Although having defended MS, I still struggle to see the point of this. Doing the two screens thing with one being a sort of keyboard is horrible, in comparison to a laptop, and is the extra screen real estate actually that useful in a protable device? If you need all that info available at once, you're probably better off at a desktop with multiple screens. Not that I'm saying nobody will want it. Just that it looks like a solution in search of a problem. Something shiny for the sake of it, rather than something to solve a burning need.
Whereas a phone that unfolds into a decent sized tablet is obviously a useful thing. I'm just not sure we've got the tech to currently do it well.