The Bug
Upgrading old worlds to 21w43a some leaves changed to surface builder blocks (grass blocks, dirt, sand, sandstone etc)
Reproduce
Create a world in 1.11.2 with the seed: 7344104151492854341
Fly towards 104 ~ -123 (You should see a swamp biome)
Leave an upgrade your world to 21w43a
Fly towards 266 ~ -80
World Download
Here is a world download from the world converted from 1.11.2 to 21w43a. Go to this location to see the issue: /execute in minecraft:overworld run tp @s 273.95 77.97 30.17 6.60 41.25
Observed Result
Some of the leaves on the swamp trees changed to dirt/grass blocks
Expected Result
The leaves wouldn't convert to grass blocks
Linked issues
is duplicated by 5
MC-239855
Grass blocks randomly placed on the old chunks
Resolved
MC-239918
Excessive abnormality between new and old world.
Resolved
MC-239921
[Blending] Funky Block Replacing
Resolved
MC-240425
New generated chunks replace tree leaves with grass dirt
Resolved
MC-240698
World can generate dirt trees (or sandstone trees etc.) when update world from 1.12.2 (or lower versions) to 21w44a
Resolved
Attachments
Comments 4
It can actually change to all surface builder blocks. So stuff like stone, granite, andersite, diorite, gravel, etc...
Can confirm in 21w43a.