When I started a singleplayer world I was in 1.7.10. I uploaded it in 1.8 to check out the new update. When I went back to 1.7.10 all of the items in my chests were gone. On all of the signs I hade, any blank rows now said "null" and all words that were on there now had quotation marks. On all signs that had a row that had And on it now said "\u0026".