The Bug:

When standing in a powdered snow cauldron, there is no freezing overlay appearing and the player takes no freezing damage.

Expected behavior:

The player/mob starts freezing, the same way as in a full powdered snow block.

The Reason:

Lava cauldrons deal lava/burning damage, water cauldrons work somewhat like water blocks (put entities on fire out / but do not give you conduit power when a conduit is nearby)