Paper/nms-patches/BlockConcretePowder.patch

--- a/net/minecraft/server/BlockConcretePowder.java
+++ b/net/minecraft/server/BlockConcretePowder.java
@@ -1,5 +1,10 @@
 package net.minecraft.server;
 
+// CraftBukkit start
+import org.bukkit.craftbukkit.block.CraftBlockState;
+import org.bukkit.event.block.BlockFormEvent;
+// CraftBukkit end
+
 public class BlockConcretePowder extends BlockFalling {
 
     private final IBlockData a;
@@ -10,8 +15,8 @@
     }
 
     public void a(World world, BlockPosition blockposition, IBlockData iblockdata, IBlockData iblockdata1) {
-        if (iblockdata1.getMaterial().isLiquid()) {
-            world.setTypeAndData(blockposition, this.a, 3);
+        if (iblockdata1.getMaterial().isLiquid() && !(world.getType(blockposition).getBlock() instanceof BlockConcretePowder)) { // CraftBukkit - don't double concrete
+            org.bukkit.craftbukkit.event.CraftEventFactory.handleBlockFormEvent(world, blockposition, this.a, 3);
         }
 
     }
@@ -45,6 +50,20 @@
     }
 
     public IBlockData updateState(IBlockData iblockdata, EnumDirection enumdirection, IBlockData iblockdata1, GeneratorAccess generatoraccess, BlockPosition blockposition, BlockPosition blockposition1) {
-        return a((IBlockAccess) generatoraccess, blockposition) ? this.a : super.updateState(iblockdata, enumdirection, iblockdata1, generatoraccess, blockposition, blockposition1);
+        // CraftBukkit start
+        if (a((IBlockAccess) generatoraccess, blockposition)) {
+            CraftBlockState blockState = CraftBlockState.getBlockState(generatoraccess, blockposition);
+            blockState.setData(this.a);
+
+            BlockFormEvent event = new BlockFormEvent(blockState.getBlock(), blockState);
+            generatoraccess.getMinecraftWorld().getMinecraftServer().server.getPluginManager().callEvent(event);
+
+            if (!event.isCancelled()) {
+                return blockState.getHandle();
+            }
+        }
+
+        return super.updateState(iblockdata, enumdirection, iblockdata1, generatoraccess, blockposition, blockposition1);
+        // CraftBukkit end
     }
 }