Worlds created with same name clash terrains

I was looking for a world with a good spawn to create a survival world with a world border, so I named it Border Survival. I spawned in the middle of a tundra with no trees, so I deleted the world and tried again with the same name. On the new world I got a better spawn and set the world border and went to look at the edge of the world. To my surprise, there were chunks from the tundra world.