Just named worlds can be mixed into each

For this bug I came quite by accident when I watched the news Pre-release version 1.4.4. The thing is that I can generate a normal world, everything is fine, but after ten minutes I found the world flown cut off part of the world to follow the sandstone plain. That did not stop me even so, sometimes it happens, although in itself it is a bug. Then I stayed with my mouth open. On the plain I discovered NPC village that was in itself lapis lazuli blogs and some iron blocks. This village, I generated in version 1.4.2 on map Superfly, the generation of the world redstone ready. Both of these worlds have been named as well, a new world. When I checked in the folder saves. Minecraft, there was only this world (the one from 1.4.2 I had already deleted a while). I attach screenshots of the game here. No mode I had installed.