Sometimes, the game does not save recent changes made to the world when the app is closed.

The first time it happened was in multiplayer LAN when I was hosting, and the next time my wife and I played she noticed a number of things she had done were reverted.

The next time it happened, it wasn't in multiplayer. I went into a cave, and signs I had placed were gone and ores I had mined were back.

The third time it happened, I was 100% certain something was wrong. I placed six furnaces to smelt some netherrack. I collected the netherrack bricks. Later that evening, the furnaces were gone and the alcove I had carved for them had reverted to a wall, but I still had my netherrack bricks in my inventory. There's no chance of it being some kind of deja vu or mistake: the evidence was in my inventory.

I cannot remember exactly how I had closed the app, whether it was quitting to the main menu, using the home screen button, or pressing the power button to turn off the screen and pause the game. But I would guess it is related to that.

I had not experienced this issue in 0.14.0. I believe it was introduced in 0.14.1 or 0.14.2. I had only played for a couple of months before the 0.14.1 update, however.