LAN Auto-Deleted World

When I logged onto my singleplayer world I added a lot of signs and command blocks and just blocks in general. When I put it on LAN I played with my friend. He was still in the world (I am pretty sure. Or he left) and then I saved the world. A few days later I load the world to copy a command from the singleplayer world to a Minecraft server and then I saw that the signs had no data and the commands had no commands and also some of my Redstone clocks and blocks had disappeared!!!!!