How to get indicator from HandleUIMessage vi to Top Level.vi

I want to custumize Simple user interface for testand (Labview). 

I read all of this:

http://www.ni.com/product-documentation/52367/en/

At the : "Handling additional events" there shows how to create callback vi so that we can do some event handling code when UI message comes:

 But If I put some boolean indicator here inside and connect it to connector pane to be used for example to indicate some event is done, i get broken Wire:

Why this is happening and how to get this indicator to the top level vi?