The application still exists in Task Manager when using Close button in Ribbon

[Nam]

Hi,

I'm using Ribbon Control for my application. When I press Close button, my application close but in task manager it still exists. 

I guess that maybe I use ShutdownMode="OnExplicitShutdown"  in App.xaml because I'd like to load My custom splash screen for this application.

Could you help me?

Thanks!