I'm playing with my friend from England via direct IP connect (not hosting a public server or anything).
We spent maybe an hour mining out the side of a rock wall. Put a fire in the cave, put some work benches just outside. Made a bunch of marble blocks.
Found a natural cave nearby, and used the marble blocks to put some stairs down them. Also put a column just outside with a torch (and torch holder) on it so we could find it again more easily.
Here's where it gets weird:
We went back to our initial camp to get more marble blocks... and the mountain had grown back (over the campfire!). We mined some of it away again just to let the light of the fire back, but it was definitely weird.
So we made more marble blocks and took them back to the natural cave.
All of our previous blocks were gone. The marble column marking its location was gone. The torch (and torch holder) now floated sadly, marking where a great pillar had once stood.
Why is everything disappearing?
I'm on a MacBook Air, OS X v10.10.3