Custom bucket

I've added a custom bucket and when i rightclick on my custom fluid, it adds the correct fluid. But when i use the normal bucket on my fluid it gives me my custom bucket instead, even when i add the normal bucket to the registry/handler.

main

CMStuff.cobaltbucket = new ItemCobaltBucket(Blocks.air).setUnlocalizedName(MODID + ":cobaltbucket_empty").setTextureName(MODID + ":cobaltbucket_empty").setCreativeTab(cobalttab);			
CMStuff.cobaltbucket_darkwater = new ItemCobaltBucket(CMStuff.darkwater).setContainerItem(CMStuff.cobaltbucket).setUnlocalizedName(MODID + ":cobaltbucket_darkwater").setTextureName(MODID + ":cobaltbucket_darkwater").setCreativeTab(cobalttab);
CMStuff.cobaltbucket_water = new ItemCobaltBucket(Blocks.flowing_water).setContainerItem(CMStuff.cobaltbucket).setUnlocalizedName(MODID + ":cobaltbucket_water").setTextureName(MODID + ":cobaltbucket_water").setCreativeTab(cobalttab);
CMStuff.cobaltbucket_lava = new ItemCobaltBucket(Blocks.flowing_lava).setContainerItem(CMStuff.cobaltbucket).setUnlocalizedName(MODID + ":cobaltbucket_lava").setTextureName(MODID + ":cobaltbucket_lava").setCreativeTab(cobalttab);


BucketHandler.INSTANCE.buckets.put(CMStuff.darkwater, CMStuff.cobaltbucket_darkwater);
BucketHandler.INSTANCE.buckets.put(Blocks.water, CMStuff.cobaltbucket_water);
BucketHandler.INSTANCE.buckets.put(Blocks.lava, CMStuff.cobaltbucket_lava);

FluidContainerRegistry.registerFluidContainer(FluidRegistry.getFluidStack("darkwater_fluid", FluidContainerRegistry.BUCKET_VOLUME), new ItemStack(CMStuff.cobaltbucket_darkwater), new ItemStack(CMStuff.cobaltbucket));

Buckethandler

/**
* Copyright (c) 2011-2014, SpaceToad and the BuildCraft Team
* http://www.mod-buildcraft.com
*
* BuildCraft is distributed under the terms of the Minecraft Mod Public
* License 1.0, or MMPL. Please check the contents of the license located in
* http://www.mod-buildcraft.com/MMPL-1.0.txt
*/
package cobaltmod.handler;

import java.util.HashMap;
import java.util.Map;

import net.minecraft.block.Block;
import net.minecraft.item.Item;
import net.minecraft.item.ItemStack;
import net.minecraft.util.MovingObjectPosition;
import net.minecraft.world.World;

import cpw.mods.fml.common.eventhandler.Event.Result;
import cpw.mods.fml.common.eventhandler.SubscribeEvent;

import net.minecraftforge.event.entity.player.FillBucketEvent;

public final class BucketHandler {

public static BucketHandler INSTANCE = new BucketHandler();
public Map<Block, Item> buckets = new HashMap<Block, Item>();

private BucketHandler() {
}

@SubscribeEvent
public void onBucketFill(FillBucketEvent event) {
	ItemStack result = fillCustomBucket(event.world, event.target);

	if (result == null) {
		return;
	}

	event.result = result;
	event.setResult(Result.ALLOW);
}

private ItemStack fillCustomBucket(World world, MovingObjectPosition pos) {
	Block block = world.getBlock(pos.blockX, pos.blockY, pos.blockZ);

	Item bucket = buckets.get(block);

	if (bucket != null && world.getBlockMetadata(pos.blockX, pos.blockY, pos.blockZ) == 0) {
		world.setBlockToAir(pos.blockX, pos.blockY, pos.blockZ);
		return new ItemStack(bucket);
	} else {
		return null;
	}
}
}

Either the normal bucket should not work or a custom normal bucket should works with my custom bucket together.