I created a new world in the latest snap shot.  After about an hour or two of playing, I started mining downward.  About a quarter of the way down (10 blocks so about 60) I can no longer pick up iron blocks.  When I go back up and try to craft, nothing happens.  

I tried to save and quit the first time and it froze on the Saving World freeze.  After navigating to another screen and coming back it returned me to the menu.  When I returned to the same world, I found the last 10 minutes I spent was gone.  After I mined back down to the iron and attempted to collect the iron ore, the same situation occurred as before.

Now as I am tying this, my game is stuck in Saving World screen and I am unable to close the window without using the Task Manager.