When you update to snapshot 14w 26c you lose bits of what you've built

Whole buildings vanished and bits of other buildings vanished when I updated to the latest snapshot. Probably best to recommend creating a new world to test the latest snapshot. Obsidian vanished. Furnaces vanished. Iron doors vanished. Some of the Acacia wood plank blocks but not others vanished. Plants in pots vanished and many other things vanished including the bed.

My comment is because I know some teenagers download the snapshots just to see the new stuff without necessarily understanding the consequences of it being alpha or beta type versions of the next update (which means there will be things go wrong like stuff vanishing- it wasn't a bother to me as I have back ups & didn't do anything I was too bothered about getting messed up by the not fully sorted out nature of the software anyway)