New worlds won't save

Put the summary of the bug you're having here

I created a new world, and built a house and a farm, and then exited to do something else. I expected to come back later and find the world in the menu.
Instead, the world was gone. Apparently it wasn't saved, somehow. I tried again, with the same result. Even in 0.7.1, I can't create new worlds.

Steps to Reproduce:
1. Create a new world
2. Exit to the main menu
3. Try to open your world again... it's gone
This bug only happens on a discontinued HP tablet.