setHelmet not working properly?

Hello, I used to make plugins a long time ago, and now I'm back to making them.
But I'm getting a lot of trouble with some simple stuff.

I'm trying to make a zoom item for a gamemode I'm working on but whenever I try to set the helmet it won't work. (I use a pumpkin, so I can use the pumpkin blur texture as a binocular texture)

Code:java

@EventHandler
public void onPlayerUse(PlayerInteractEvent e){
if(e.getPlayer().getItemInHand().getType() == Material.QUARTZ){
RPPlayer rp = RPGame.getRPPlayer(e.getPlayer());
Player p = e.getPlayer();
rp.zoom++;
if(rp.zoom==2){rp.zoom=0;}
if(rp.zoom==0){
//Reset all zoom
p.removePotionEffect(PotionEffectType.SLOW);
p.setWalkSpeed(0.2f);
if(rp.preZoomHelmet!=null){
p.getEquipment().setHelmet(rp.preZoomHelmet);
}
}
else if(rp.zoom==1){
//Zoom small
p.removePotionEffect(PotionEffectType.SLOW);
PotionEffect zoom = new PotionEffect(PotionEffectType.SLOW,99999,255);
p.addPotionEffect(zoom);
p.setWalkSpeed(-0.25f);
rp.preZoomHelmet = p.getEquipment().getHelmet();
p.getEquipment().setHelmet(new ItemStack(Material.PUMPKIN));
}
}
}

The event is registered correctly, because the zoom itself works.
I think the only important part for this problem is the last 2 functions.
There are also no errors, and I also tried
p.getInventory().setHelmet, but no succes with that either.

I'm running the 1.7.9 development build (R0.1 build 3075)

I found out that it does set it, but doesn't update the players inventory for some reason.
What's up with that?

EDIT:

Fixed using the updateInventory method, but that is deprecated...

EDIT by Moderator: merged posts, please use the edit button instead of double posting.