5/8 of Minecraft PE world GONE with new update

[So I've been working on a Minecraft "Old" world since 2013, it's virtually the only world I ever play in, and after the new update 5/8 of it is gone. The edges of the world, which used to be at x=0 and 255 and z=0 and 255, are now at x=-64 and 191 and z=-128 and 127. I have no idea why it did this but it is incredibly annoying as I have lost years of work.

I uploaded a YouTube video to show what has happened to my world if you're interested:

https://youtu.be/uJ616wiUFLg