Using 1.20.4 client on 1.21.4 server causes water ghosting

[viimeinen1]

'/viaversion dump' Output

https://dump.viaversion.com/1b05c7b5e0aa836db188599a67348c2fd83d93e9323d649a6d83225aa7dcf3dd

Server/Client Error

No errors; gameplay issue.

Bug Description

Placing water on the edge of your reach causes desync where water is placed client side, but not server side when using version 1.20.4. This does not happen on 1.21.3 or 1.21.4 when server version is 1.21.1 or 1.21.4.

Steps to Reproduce

1. Have a 1.21.1-1.21.4 paper server with ViaVersion and ViaBackwards installed
2. Join on 1.20.4
3. Have water bucket on survival
4. walk backwards and place water as far as possible you can.
5. The water should ghost (not always, but enough to affect pvp over multiple hours, and enough to recreate)

Expected Behavior

Water shouldn't ghost, as it does on client versions 1.21.3 and 1.21.4

Additional Server Info

Tested with both velocity proxy (3.4.0-SNAPSHOT (git-4aa9ee77-b455)) and without proxy. Both have same issue.

I removed all other plugins except ViaVersion and ViaBackwards

Checklist

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

[Barvalg]

[viimeinen1]

Here is a clip of the water ghosting:

https://github.com/user-attachments/assets/f2d3d9e2-2669-475a-a287-dc82171765c0

Client version was 1.20.4 (using fabric)