Note: while this behaviour has been the case for many updates in Bedrock Edition, this is still a valid request as this functionality has only been added to Java Edition in the latest snapshot.

In Bedrock Edition, attempting to add water from a bucket to an existing lava cauldron will result in steam particles, a loud hissing noise, and the cauldron being fully emptied. The same result can be obtained from adding lava to an existing water cauldron.

In Java Edition, however, the fluid within is just directly replaced.

Bedrock Edition also allows water from water bottles to be added to lava cauldrons, producing this exact same result - however, attempting to do so in Java Edition just makes you drink the water bottle instead.

Other version differences with cauldrons exist, notably the transparency of water in cauldrons (which was removed from Java for an unknown reason), the ability to dye water in cauldrons (used for leather armor dyeing - implementing this would allow for the crafting recipe to be removed, eliminating another NBT-dependent crafting recipe), and storing potions in cauldrons (which can be found naturally in witch huts). However, these features have been in Bedrock Edition since before Buzzy Bees and as such are not acceptable parity requests.