Can place cauldron with lava under the water.

Thank you for your report!
However, this issue is Working as Intended.

The report you have submitted is working as intended: https://feedback.minecraft.net/hc/en-us/articles/360020324051-Minecraft-Beta-1-9-0-2-Xbox-One-Windows-10-Android-.

Cauldrons can now be used to hold Lava

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Things such as graphics, sounds, world creation, biomes, redstone, villagers, and animals may not work the same in current versions.

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I don't understand, are you say that it's normal that cauldron with lava can be placed under water?