My daughter logged into her minecraft today (version says 0.8.1) and found that all players' chests were invisible. They clicked where the chests were supposed to be, and the chests re-appeared, but they were empty. They had previously been filled with important materials that had been saved over long periods of play time. Why did this happen and how can we be sure it will not happen again? PLEASE NOTE: I am not sure about the version, but she plays a pocket edition on an ipad mini that she bought new three months ago.