I used the toast notifications for desktop app since Windows 8.1 but with the new action center in Windows 10, I am experiencing some unexpected behaviours.
When the
Win32 apps need to set up a COM server in order to have toasts persisted in Action Center: http://blogs.msdn.com/b/tiles_and_toasts/archive/2015/10/15/quickstart-handling-toast-activations-from-win32-apps-in-windows-10.aspx
An alternative to the COM method is to set a registry key for your app. Replace irssi with ToastDesktop in your case.