When renaming an item on the anvil and deleting all characters of its name, the anvil output is not updated.
This is primarily a nuisance when deleting all characters in a renamed item's name to revert to the default item name.
How to reproduce:
Put an item onto the anvil and remove all but a single character in its name: The item name is updated in the output slot.
[media]
❌ Remove the last character left in its name: The output slot is not updated.
Insert any character, even space, to update the output slot.
You can also get the issue when you remove multiple selected characters at once:
Put an item onto the anvil and delete some characters from its name: The item name is updated in the output slot.
[media]
❌ Select all characters left in its name and press backspace: The output slot is not updated.
[media]
Insert any character, even space, to update the output slot.
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This report is well written, but it is a duplicate of MC-124327.