I upgraded a "Caves" type generator World to 21w44a and when I went under the world I saw that the bedrock was replaced with Deepslate, but it said be bedrock since the height of Caves world is still 0-128. Then I went to the edge where the new chunks are and I saw that the world tried to blend and it created chunk error walls.

How to reproduce
1. Create a Caves generator world in 1.17.1 or below
2. Generate some chunks in 1.17.1 or below
3. Save the world and load up 21w44a
4. Load up the Caves world you generated in 1.17.1 or below
5. X World blending is broken and Bedrock is deepslate in old chunks