If you turn on hardcore mode with cheats activated before creating a world, the cheats will turn off, but the game will say that you need to turn cheats off to earn achievments.

Steps to reproduce:

1. Click "Play" and create a new world
2. Turn cheats on
3. Turn hardcore mode on   
4. Start the world

Observed Results

• Achievements remain disabled.
• Cheat commands are available in the world.

The cheats will be off, but the game will say you need to turn cheats off to get achievments.

Since cheats are off it should not tell you to turn off cheats.