Upgrading old worlds causes leaves to change to surface builder blocks

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