Dug a large tunnel bringing up large amounts of cobblestone (approx 500) exited app to pull up a YouTube video. When I went back to MCPE all of the stone was back where I had tunneled. Placed blocks stay however. This completely blocks any mining and makes you have to remine everything each time you log into your world. Besides providing a new form of infinite place-able blocks exploit, this glitch ruins the ability to get the rarer ores such as diamond, unless someone would like to sit and grind for them for hours (doubtful).