Minecraft: Fancy Cliff

I started a Flat World game not too long ago while playing Minecraft and at first, everything was normal. I found an NPC village, decided to make my home there and spent most of my time running around killing sheep. When a new version of the game got updated and my Flat World converted to that newest version, I found myself in the ground, suffocating. When I re-spawned it was in a little cave. What's more weird, I re-spawned in the air, got fall damage, and the mouth of the cave I was in showed the bright blue sky. However, the cave was on a laaaaaaaaarge cliff-side. Thankfully, there was a waterfall right below the cave entrance so I just safely made my way down to the ground.

So here I am, in a 'Flat World' with a huuuuuuuuge cliffside that goes on for miles. The ground acts as if I'm around 5 blocks from the bottom of the world (the particles float in the air) but I'm not exactly sure how this happened. When I looked it up, it appeared to be a glitch in the 12w05b version of the game (Whatever the hell 12w05b is. Does it mean it's version 1.2.5?) and it happens when you go off the map. The rest of the world tries to spawn like it would in a normal game, or whatever.

Unfortunately, when I was modding I didn't have a backup copy handy for when I made mistakes, so when I tried to get my thing back it after doing something stupid it completely died. So this world is gone. D:

I've been trying to re-create it, but I'm not sure how. Anyone have any ideas for me? I'd like to get this cool glitch back