yesterday I've done some mining. On my solo deed. Nobody else has an access.
When I logged off yesterday I left some of the mined stone shards in piles inside the mine.
When I logged in today, I noticed a rock shard on the surface. I'm 100% sure it wasn't supposed to be there.
The shard was acting very strange, I was unable to pick it up. There was an option to pick it up, even character animation of picking has been shown, but the shard stayed on the ground anyway.
I tried to relog, the same results.
Eventually I dropped some items on the tile to create a pile and managed to pick up the shard finally.
Then I realized that there's a pile of shards on the same exact tile underground and the weird shard just must've traveled to the surface overnight somehow.
I don't think I can reproduce this, but you should probably take a look at this strange phenomenon.
Edit: Since it was just 1 shard, I'm thinking maybe it was the shard I analyzed and put back inside the mined pile? Just an idea.
Edit 2: Some additional info - I've done some corner raising (using concrete) and ceiling mining on one tile border of the tile in the mine. Maybe it contributed to this strange behaviour somehow?
Edit 3: It may as well be a client bug, who knows?