I'm having the same problem and would really like to see an answer here! One difference that I noticed is that if you run a "Silverlight Project" from VS Orcas it tries to navigate to a file path, whereas if you run an ASP.NET project it starts the local
web server and navigates the browser to http://localhost/MyProject. So, how can we make a Silverlight project know that it needs to launch through the local web server instead of just navigate to a file path?
It would still be nice to get an answer here, but my workaround is to open the project as if it were a web site. This fixes most issues but it still doesn't explain why creating a new Silverlight project doesn't cause run to work as expected.