World deletion fails

Create a new non-flat world, give it a sample name like "testworld"

leave to menu, delete this world

looking to the saves folder shows you, the world is not deleted

creating a new world, give it exactly the same name as the first one, but change it to be a superflat one

loading this world results in either loading the old one, or loading mixed chunks from the non-flat and the flat one, like on the screenshot