Incorrect block rendering with Minecraft 1.9 client

[lolplay123]

'/viaversion dump' Output

https://dump.viaversion.com/06cad65c70985b1f8f31e3a124474667653a171675f09a11fa2db251f0fe1009

Server/Client Error

No errors or warnings are shown in the server console or client.

Bug Description

When connecting to a Paper 26.2 server using a Minecraft 1.9 client through ViaVersion and ViaBackwards, some blocks are rendered incorrectly.

The issue occurs when loading chunks, and the affected blocks do not appear to be rendered correctly.

No errors or warnings are shown in the server console or client.

Steps to Reproduce

1. Set up a Paper 26.2-build 124 server.
2. Install ViaVersion 5.12.0-SNAPSHOT+1057 and ViaBackwards 5.12.0-SNAPSHOT+626.
3. Connect to the server using a Minecraft Java Edition 1.9 client.
4. Load chunks by joining the server and moving around the world.
5. Some blocks are rendered incorrectly.

The issue occurs with Version 1.9.

Version 1.9.1 does not reproduce the issue.

Additional Server Info

The issue was first noticed on a Paper server running behind a Velocity proxy.

For testing, I also ran the Paper server without Velocity and confirmed that the issue still occurs when connecting directly to the Paper server.

The only plugins installed on the Paper server are:

ViaVersion 5.12.0-SNAPSHOT+1057
ViaBackwards 5.12.0-SNAPSHOT+626

Checklist

• Via plugins are only running on EITHER the backend servers (e.g. Paper) OR the proxy (e.g. Velocity), not on both.
• I have included a ViaVersion dump.
• If applicable, I have included a paste (not a screenshot) of the error.
• I have tried a build from https://ci.viaversion.com/ and the issue still persists.

[Barvalg]

Athena Log Analysis

Platform Information:

Property	Details
Contains Via	❌
Platform Type	unknown
Is Proxy	❌

[roccodev]

fwiw I had a similar issue when manually setting all block light in a chunk to be 15, might be related (and still would only affect 1.9)