The other day, I noticed that my windows weren’t behaving correctly. Alt-tab didn’t tab between windows; the minimize button wasn’t working; the window-right-arrow to make a window take up half the screen wasn’t working… it was driving me absolutely batty. I just assumed it was due to some goofy upgrade and that I’d have to learn to live with it.
It turns out, somehow, “tablet mode” had gotten switched on. To toggle tablet mode on and off, click the thing on the task bar that looks like a speech bubble. You’ll see a bunch of boxes on the bottom of the panel that opens, and yeah, one of them says “tablet mode.” Just click it and all your problems are solved.