Update firework power when modifying meta. Fixes BUKKIT-3272

src/main/java/net/minecraft/server/EntityFireworks.java

@@ -3,7 +3,7 @@ package net.minecraft.server;
 public class EntityFireworks extends Entity {
 
     private int a;
-    private int b;
+    public int b; // CraftBukkit - private -> public
 
     public EntityFireworks(World world) {
         super(world);

src/main/java/org/bukkit/craftbukkit/entity/CraftFirework.java

@@ -11,6 +11,8 @@ import org.bukkit.entity.EntityType;
 import org.bukkit.entity.Firework;
 import org.bukkit.inventory.meta.FireworkMeta;
 
+import java.util.Random;
+
 public class CraftFirework extends CraftEntity implements Firework {
     private static final int FIREWORK_ITEM_INDEX = 8;
 
@@ -54,5 +56,9 @@ public class CraftFirework extends CraftEntity implements Firework {
 
     public void setFireworkMeta(FireworkMeta meta) {
         item.setItemMeta(meta);
+
+        // Copied from EntityFireworks constructor, update firework lifetime/power
+        Random random = new Random();
+        getHandle().b = 10 * meta.getPower() + random.nextInt(6) + random.nextInt(7);
     }
 }