Unable to Rename Items in Anvil

[strad-dev]

Expected behavior

When an item is in the first anvil slot and the second slot is empty, I should be able to rename the item.

Observed/Actual behavior

• The Anvil GUI resets each keystroke. The name at the top gets reset back to whatever the item's original name was.
• The resultant item contains the last keystroke's changes.

Steps/models to reproduce

1. Place a clean Netherite Sword into the first slot. Leave the second slot empty.
2. Type ! into the item's name field.
3. Observe that the name field gets reset to "Netherite Sword" while the output item is renamed to "Netherite Sword!"
4. I would expect the name field to stay as "Netherite Sword!"

Plugin and Datapack List

Issue occurs even with no plugins. Server has BlazeandCave advancements datapack.

Paper version

This server is running Paper version 1.21.11-126-main@3f5728e (2026-02-28T11:49:07Z) (Implementing API version 1.21.11-R0.1-SNAPSHOT)
You are running the latest version
Previous version: 1.21.11-116-6f71be8 (MC: 1.21.11)

Other

No response

[Doc94]

Cannot replicate... a freash server with that datapack and the anvil works like expected for rename.

[strad-dev]

Weird. Could it be some residual data leftover from plugins?

[Doc94]

Weird. Could it be some residual data leftover from plugins?

unless any modify the item i dont see a way a removed plugin can cause that issue.

[strad-dev]

I did have a plugin that contained a patch for another issue where items interacted with in Creative had some sort of extra empty components, which made them unstackable with items obtained in survival. That plugin stripped the empty data, but I don't see how this could cause anvil renames to fail? Unless I'm doing something weird.

The code that does this is on GitHub, but it's very messy.

[Doc94]

If you still has issues maybe can go to Discord for help, but the main issue cannot be replicated in fresh server.

[strad-dev]

Ok. I'll open another ticket for the upstream issue that caused me to code a workaround that caused the issue described in this ticket.
I was able to reproduce the former on a fresh server.

[strad-dev]

Actually, ignore that. This was all caused by one of my client-side mods. My bad.