This happens to me too. Some details: iOS 7. iPhone 4. It happens with not just diamonds. It seems to happen to things you've recently put in the chest just before closing the app. I've lost bows, iron, gold, doors, rails, etc. if you for example add 7 iron to chest and some rails then close app and come back in then all rails and iron in that chest might be gone including stuff of that type that had already been there. This happens frequently, but not all of the time. It started in version 0.8.0 I think and is still there in 0.8.1. I've seen it in single player survival in safe mode.
Michael Henke
MCPE-6671
This happens to me too. Some details: iOS 7. iPhone 4. It happens with not just diamonds. It seems to happen to things you've recently put in the chest just before closing the app. I've lost bows, iron, gold, doors, rails, etc. if you for example add 7 iron to chest and some rails then close app and come back in then all rails and iron in that chest might be gone including stuff of that type that had already been there. This happens frequently, but not all of the time. It started in version 0.8.0 I think and is still there in 0.8.1. I've seen it in single player survival in safe mode.