[MC-210285] Item duplication when holding down 0-9

Holding down a key to switch an item to another inventory slot while hovering over it in the inventory sometimes causes the item to duplicate.

For an example, see https://youtu.be/yVnveKIz0n0. I hold down 9 while mousing over the sword. The bug seems to be more consistent at higher render distances (i.e. lower frame rates). It took multiple minutes of holding the button down to trigger the bug at a render distance of 3, for example.

UPDATE: Reproducing the bug on a pure vanilla (non-Optifine) version of Minecraft: https://youtu.be/GClXqYVNqbg

The bug took considerably less time to trigger, further suggesting that it is tied to framerate (Optifine being a performance-enhancing mod).

Also of note is that sometimes it isn't the item that gets duplicated but rather the blank hotbar slot one is swapping it with: https://youtu.be/ZGc7drZPRIE

Comments 2

violine1101 2021-01-02T14:22:42Z

We do not have enough information to find the cause of this issue.

Please record a video of this happening and attach it to this report.
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violine1101 2021-01-02T15:47:50Z

Thank you for your report!
However, this issue is Invalid.

Your game, launcher or server is modified.
If you can reproduce the issue in a vanilla environment, please recreate the issue.

Any non-standard client/server/launcher build needs to be taken up with the appropriate team, not Mojang.
Any plugin issues need to be addressed to the creator of the plugin or resource pack.
If you have problems on large servers, such as The Hive and Hypixel, please contact them first as they run modified server software.

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