What method is used to update a player's active item? Not the UpdateActiveItem(uint)?

private void OnActiveItemChanged(BasePlayer player, Item oldItem, Item newItem){
	if(newItem.info.shortname == "explosive.timed"){
		player.UpdateActiveItem(oldItem.uid);
	}
}

You may also try setting old item's held entity stuff like whether its held.

But does this method no already do that?

	HeldEntity heldEntity = activeItem.GetHeldEntity() as HeldEntity;
	if (heldEntity != null)
	{
		heldEntity.SetHeld(false);
	}
        Item activeItem2 = BasePlayer.GetActiveItem();
	if (activeItem2 != null)
	{
		HeldEntity heldEntity2 = activeItem2.GetHeldEntity() as HeldEntity;
		if (heldEntity2 != null)
		{
			heldEntity2.SetHeld(true);
		}
	}
}