Started up minecraft, made minecraft window full screen on 2nd monitor (NOT full screen in-game, still had windowed border). 2nd monitor is portrait 1200x1600. Buttons didn't work for starting up game, only ones on the lower part of screen worked. Only solution is to change resolution to use the gui.

NOTE: In picture, my mouse was hovering over the brick block tab, but the game thought I was hovering over the stone.

Gui settings set to Auto, but I did try large as well. No dice.