Hardcore-world isn't marked as 'hardcore'?

Hello, I wanted to play with hardcore experience. I died at the first night... But I could respawn! I clicked on the 'Main menu', to see whether the world as 'Hardcore' are marked; it wasn't! I attached a screenshot, on which you can see that I wanted to use the world as hardcore world wanted to use. I tried again and it happened the same thing!

Does anyone know of a similar/same problem and can any one help me with it?