So if you are standing on a block and you change to spectator mode, then change back to creative, the game crashes! I attached the crash report. This is in singleplayer by the way... this bug would be great to get fixed because I plan on using barriers a lot...
Environment
Java 7 Update 45, Windows 8.1, 3G of ram for Minecraft, intel core i5, Nvidia geforce gt 635m 2g
Duplicate of MC-46408