The bug
After creating a new hardcore world, the buttons Allow Cheats and Bonus Chest are supposed to be locked/disabled (greyed out).
However, if you choose Superflat or Buffet as the world type and press Customize, the next time you join this screen, all the buttons will be unlocked/enabled, but you can't change the value of the buttons mentioned above.
How to reproduce
Make a new world
Set game type to Hardcore
Go to More World Options
Select Superflat or Buffet, and hit Customize and head back
→ ❌ The options for Allow Cheats and Bonus Chest aren't greyed out
Linked issues
is duplicated by 16
MC-10182
Hardcore greyed out buttons re-activated after superflat customization
Resolved
MC-12004
button state changes while flipping through the settings of create world
Resolved
MC-16375
Hardcore locked buttons get unlocked after entering Superflat Customisation
Resolved
MC-30553
Strange World Options Textures
Resolved
MC-62546
Hardcore Mode Restraints Not Showing
Resolved
Comments 13
Affects 19w02a.
To put it more simply, selecting 'Hardcore', clicking 'Customize' on Superflat or Buffet world generation, then going back unlocks the 'Allow Cheats' and 'Bonus Chest' buttons, even though you can't change their settings.
Still happens in 13w38c.