ASP.NET 5 - beta8: no rebuild in background

Before beta8 it was possible to start a Web Application, change some of the code (e. g. the ViewBag.Message of the About-View), save and refresh the browser - voilá, the new Message is displayed without rebuilding the project. This is explained in the Tutorial of ASP.NET 5 as well.

Now when creating a new Web Application with beta8 which uses DNX and Kestrel this seems no longer to work. Any idea why?