After reducing the window size and later launching the demo again, it initially opened the correctly sized window, then made the window fill the screen. Going into the options, I could get it back to the size I wanted by opening and closing the size menu (without changing the selected value).

Controller seems to only be recognized if connected at launch, and only for as long as it stays connected. Having to connect it before launch isn't really a problem for me, but having to quit and relaunch the demo if the controller goes to sleep is annoying as the demo only saves at specific checkpoints.