Old World Crashes when loading

I have updated to Minecraft 1.6.0 on my ipad.

Playing the game I noticed frequent crashes in my pre-1.6 world. I was usually able to reload the world.

Then I noticed that the crashes seem to appear when I cross a certain line in my world on my way to one of my villages. I was still able to reload my world but it always crashes at the same place. 

Then I entered the Nether and went to a Nether Portal which is beyond this crash line in the Overworld. That worked fine. I entered the Overworld through that Nether Portal beyond the crash line, which worked for a few seconds, but then Minecraft crashed again. 

Now I cannot load my world any longer, The loading bar completes but the world immediately crashes Minecraft. This makes my existing world unusable. 

Creating a new world in 1.6.0 seems to be working fine. 

On a side note, I noticed that during one of the crashes I was riding a horse. The horse is gone now. I also noticed that my Ice Bear that I had in my zoo is also missing after one of the crashes. 

Kind regards

DocMacz