This one is very obvious in itselve but I will do into detail. I went into options then Video Settings the moment I slide the 'Resolution' bar to start playing Minecraft, for best FPS performance when I about to play, that's when my mouse got displaced up by 1 1/2 inches away from the actual cursor.
I didn't took a screenshot but this can be replicated easily the moment you mess with the Resolution slide bar.
I can't reproduce this. Please attach repro steps or screenshots.