Water seems to be bugged in the latest preview. Unlike in the 1.21.51 Hotfix or 1.21.4 for Java, Water no longer interacts correctly with blocks that generate bubble columns. These include Magma Blocks and Soul Sand Blocks (it could affect other blocks but that requires more through testing on my part).

Steps to reproduce:

1. Launch Minecraft Preview (1.21.60.27)
2. Create a new world in creative mode
3. Place down a Magma Block or Soul Sand block.
4. Empty a Water Bucket on the block you just placed

Expected Result:

Water naturally flows from the Water Source Block on the Magma Block or Soul Sand block and onto the ground.

Observed result:

Water does not flow from the Water Source Block and onto the ground even after its updated by placing a block. It is only updated when it touches flowing water from another source.