Saved Hotbars cannot be saved in Creative mode (C + number does nothing, no log output)

In Minecraft Java Edition 1.21.x, the Saved Hotbars feature does not work in Creative mode.

When opening the Creative inventory → Saved Hotbars tab and pressing the save key combination (C + 1–9, or any rebind), nothing happens.
There is no visual feedback, no error message, and no related output in latest.log.
The hotbar is not saved and the slot remains empty.

This happens consistently and appears as if the save action is never triggered.

Reproduction steps:

1. Launch Minecraft Java Edition (latest 1.21.x)

2. Create or load a Creative mode world

3. Open the Creative inventory (E)

4. Open the Saved Hotbars tab

5. Place items in the hotbar

6. Press C + 1–9 to save

7. Exit the game

Expected result:
The current hotbar should be saved into the selected Saved Hotbar slot.

Actual result:
Nothing happens; the hotbar is not saved.

What was tested and ruled out:

• No mods (pure vanilla)

• Rebinding save hotbar keys

• Windows on-screen keyboard (osk)

• Deleting hotbar.nbt and letting it regenerate

• Newly created worlds

• Hotbar number keys work normally for hotbar switching