I was finishing my house when a creeper comes and killed me. After that, i wanted to create a new Hardcore world but I saw that the old world in hardcore wasn't deleted and i actually can go in again.

What I expected was that the world was deleted when I died and click on the "Delete World" button.

What happened was that the world is playable after doing that without doing anything special.

Steps to reproduce:
1. Create a Hardcore world
2. Die
3. Click on the two buttons that appear on the screen
4. Go to Singleplayer and you will be able to continue your Hardcore map.