[solved] Items disappearing from LivingDropsEvent?

While adding items to LivingDropsEvent's drops list, I noticed that sometimes when I killed the mob my item would spawn, but then quickly disappear. Using spawnEntityInWorld directly from the event has the same effect.

EntityLivingBase mob = event.entityLiving;
ItemStack orb = getOrbDrop(mob); // this just returns an itemstack to drop
if (orb != null) {
// tried this one first:
event.drops.add(new EntityItem(mob.worldObj, mob.posX, mob.posY, mob.posZ, orb));

// then I tried the following instead:
mob.worldObj.spawnEntityInWorld(new EntityItem(mob.worldObj, mob.posX, mob.posY, mob.posZ, orb));

// both with the same result
}

I thought it might be something to do with spawning the item directly on the mob's position, getting cleared when the mob is marked for removal or something like that, but in the entityDropItem method that's exactly how they create the EntityItems, so... what's going on here?

EDIT: Figured it out. If I use 'copy()' on the ItemStack when I construct the EntityItem, everything works as intended. I suppose that's what I get for using a static method to return my ItemStack

// working code
mob.worldObj.spawnEntityInWorld(new EntityItem(mob.worldObj, mob.posX, mob.posY, mob.posZ, orb.copy()));