/item replace into armor slot with non-armor items (e.g., Glass) corrupts armor attribute

Steps to Reproduce

1. Start a Vanilla Minecraft Java Edition server (version 1.21.11 confirmed).

2. Join the server with operator (OP) permissions.

3. Ensure your character's armor slots are empty. You can verify the baseline armor value by executing: /attribute @s minecraft:generic.armor get (It should return approximately 0.0E-7).

4. Execute the command to force a non-armor item into the helmet slot: /item replace entity @s armor.head with minecraft:glass

5. Immediately query the armor attribute again: /attribute @s minecraft:armor get

6. Manually remove the glass from the helmet slot via the inventory.

7. Query the armor attribute a third time: /attribute @s minecraft:armor get

What I expected to happen :

• The glass item, not being armor, should not be equippable in the armor slot or should contribute zero armor points.

• After removing the glass, the player's armor attribute should return exactly to its correct baseline (0).

What happened instead:

• After step 4 and step 5: The armor attribute value becomes 11.0 (which equals 11 armor points, visually increasing the armor bar). This is an incorrect, massively inflated value.

• After step 6 and step 7: The attribute value does not reset to zero. It persists at an incorrect residual value (e.g., 2.0E). This proves a state corruption.

Additional Information :

• Severity : This bug allows players with command access to grant permanent, unfair armor bonuses, breaking survival mode balance.

• Environment: Reproduced on an Aternos-hosted Vanilla server, confirming it is a bug in the official Mojang server software.

• Suggested Fix : The /item replace command (or the underlying game logic) should validate that an item belongs to the armor category before allowing it to be placed in an armor slot and before calculating its attribute contributions.