I was making a redstone video for my youtube channel. It is about a redstone banking system. In the process of recording, I was showing the viewers that it doesn't take items that don't belong in the system. You put an incorrect item in, and it will go all the to the dropper in the top. It dropped the item on the floor, and when I picked it up, it went into slot 1, and deleted my diamond which was in there. I checked my survival inventory, and it wasn't there either. I haven't been able to reproduce the bug ever since that. Here is a link: http://youtu.be/GcRFhMflJW0?t=1m10s