Anvil GUI doesn't update immediately after gamemode change

The bug

If you try to change your gamemode from survival to creative while holding some random item and enchantment book in anvil GUI it still stays unenchantable, it should update.

How to reproduce

1. Setup a command block with a delay to run /gamemode creative @p.
2. Take some random stuff and enchantment book.
3. Change your gamemode to survival, and press the button.
4. Quickly open the anvil, and place items in slots.
5. Wait for command block to run command.
   → The result in anvil is still unavailable
6. Remove and place any item again.
   →  Notice you can now enchant your unenchantable item