Game crashes while loading worlds and placed blocks disappear when you exit

When I started a world any structures/ blocks made or placed on creative disappear when the world is closed and restarted I have seen this on the iPhone 5 and iPad mini. This may occur for all iOS devices. If you have also experienced this please comment and leave a comment if there is a way to fix this because I cannot build on any of my creative worlds. The only device it hasn't happened to me not is the iPod 4. But I only have played it on the iPod 4, iPad mini, and the iPhone 5. Also on all devices the game will load a world and before the loading bar pops up it freezes then crashes.