I was working on my adventure map, (good thing i had a backup) and after i logged out of the world (i work in singleplayer) and then logged back in after some time one big part of a chunk was missing, as in being turn to air blocks, i'm glad none of my command blocks were in that chunk, so i just rebuilt it, next time a day later same thing happens but not behind my back, this time the part of a chunk that dissapeared was very close in front of me.

i really don't know how to replicate this because it didn't happen every time that i logged out and back in, but this has only been happening in 14w30 versions.

P.S. i checked whether or not it could be any of my command blocks doing this but unfortunately not a single one had a command that would come even close to deleting those random parts of my world.