In the controls menu, if click on the buttons for attack, use item, or pick block, which are labeled Button 1, Button 2, and Button 3 respectively, and then click off the block, they will change to all either Button 1, or two to Button 1 or 2, and the other to Button 1 or 2. There is no way to change it back to the default, and if you click done, you can't use any items, attack, mine, or place blocks! So frustrating!