[Question] About mixin, template and alias

[Michael]

/////// fire.d

import std.stdio;

alias void delegate() EventHandler;

class Event(T)
{
     private T[] _events;

     public void opOpAssign(string op)(T param) if (op == "~")
     {
         writeln(param.funcptr);
         _events ~= param;
     }

     public void opCall(ParamType ...)(ParamType params)
     {
         emit(params);
     }

     protected void emit(ParamType ...)(ParamType params)
     {
         foreach (event; _events)
             event(params);
     }
}

mixin template AddEvent(DelegateType, string member)
{
     auto eventObserver =  new Event!DelegateType();

     mixin("alias eventObserver " ~ member ~ ";");
}

class Fire
{
     public mixin AddEvent!(EventHandler, "click");
}

/////// water.d
import std.stdio;

import fire;

class Water : Fire
{

}

void main()
{
     auto fire  = new Fire();
     auto water = new Water();
     water.click ~= () { writeln("Water!"); };
     fire.click  ~= () { writeln("Fire!");  };

     fire.click();
}


Output:
Water!
Fire!

Someone can explain me a behaviour of above code? Why not "Fire!" 
only?