If your hotbar is full of items and you have another item in the upper left corner and you delete all the items with the function inside the creative inventory (the cross to the right), the upper left item isn't deleted.
It works correctly when you have your whole inventory full.
This issue has been in the game for a long time.
I couldn't find any matches of this issue in the Java Edition inside this webpage.
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Duplicate of MC-156857

Duplicate of MC-156857