PaperMC/paper-server/nms-patches/net/minecraft/world/level/block/BlockCauldron.patch

--- a/net/minecraft/world/level/block/BlockCauldron.java
+++ b/net/minecraft/world/level/block/BlockCauldron.java
@@ -11,6 +11,10 @@
 import net.minecraft.world.level.material.FluidType;
 import net.minecraft.world.level.material.FluidTypes;
 
+// CraftBukkit start
+import org.bukkit.event.block.CauldronLevelChangeEvent;
+// CraftBukkit end
+
 public class BlockCauldron extends AbstractCauldronBlock {
 
     private static final float RAIN_FILL_CHANCE = 0.05F;
@@ -51,11 +55,11 @@
     @Override
     protected void a(IBlockData iblockdata, World world, BlockPosition blockposition, FluidType fluidtype) {
         if (fluidtype == FluidTypes.WATER) {
-            world.setTypeUpdate(blockposition, Blocks.WATER_CAULDRON.getBlockData());
+            LayeredCauldronBlock.changeLevel(iblockdata, world, blockposition, Blocks.WATER_CAULDRON.getBlockData(), null, CauldronLevelChangeEvent.ChangeReason.NATURAL_FILL); // CraftBukkit
             world.triggerEffect(1047, blockposition, 0);
             world.a((Entity) null, GameEvent.FLUID_PLACE, blockposition);
         } else if (fluidtype == FluidTypes.LAVA) {
-            world.setTypeUpdate(blockposition, Blocks.LAVA_CAULDRON.getBlockData());
+            LayeredCauldronBlock.changeLevel(iblockdata, world, blockposition, Blocks.LAVA_CAULDRON.getBlockData(), null, CauldronLevelChangeEvent.ChangeReason.NATURAL_FILL); // CraftBukkit
             world.triggerEffect(1046, blockposition, 0);
             world.a((Entity) null, GameEvent.FLUID_PLACE, blockposition);
         }