Hardcore locked buttons get unlocked after entering Superflat Customisation

When you create a new hardcore world, the buttons "Allow Cheats" and "Bonus Chest" are supposed to be locked/disabled (dark grey).
Although, if you choose Superflat as the world type and press Customise, the next time you join this screen, all the buttons will be unlocked/enabled, but can't change the value of the buttons mentioned above.

~CurseLuke (@ YouTube)