Trying to inject IEventAggregator in Prism Shell not working -- ideas?

See more:

C#

WPF

PRISM

I have my bootstrapper creating an instance of the shell:

protected override DependencyObject CreateShell ( )
{
    MainWindow shell = new MainWindow( this.Container.Resolve<IEventAggregator>( ) );
    return shell;
}

protected override void InitializeShell ( )
{
    base.InitializeShell( );

    App.Current.MainWindow = (Window)this.Shell;
}

and I have my shell consuming the constructor:

public MainWindow(IEventAggregator aggregator)
{
    InitializeComponent( );
    this.DataContext = this;
    this.eventAggregator = aggregator;
    eventAggregator.GetEvent<BusyIndicator>( ).Subscribe( SetIndicator, ThreadOption.UIThread );
}

However I found two issues: the framework wanted to call the empty constructor and I kept getting a null exception until I added an empty constructor to the Shell.
Then I added a test in that logic to Assert if the initialized IEventAggregator ended up to be null. No surprise here it was null. So for some reason even though InitializeShell() was called and the window was set, it was recreated by the system (Prism?).

Any suggestions on how to inject the event aggregator into the shell of my prism application? Should I not call base.InitializeShell() ??? (though the call to the empty constructor of the shell occurs after the BootStrapper.Run command was executed) I'm building it as a WPF application under the 4.0 framework using Prism 4.1 and Unity 2.0.