For some reason, every few months or so this happens to me and I have to completely re install minecraft to fix it. My crafting gets messed up. Its hard to describe, but the way it just operates is weird. Dragging blocks is delayed, things glitch, but the most annoying element is that i cannot use the shift key to automatically craft things. Also, I've noticed some odd graphical errors. Anyone know how to prevent this from happening? I already know I have to re install minecraft. But this is a re occurring problem, so I don't want this to happen again.