Biomes being partially overwritten / regenerated in 1.20pre2 inside old world

The attached screenshots show portions of a desert and savanna biome that were generated in version 1.19.4, and the same areas in version 1.20 pre2.  In the 1.20 pre2, the area was partially regenerated / overwritten by various ocean biomes (Cold Ocean, Deep Cold Ocean).

This causes a change in foliage color and sharp chunk boundaries between biomes.  In this case, much of the pre-existing Desert biome (sand) collapsed into the ocean upon loading of the area in 1.20 pre2.

This was observed in a preexisting / old (pre-1.19) world.