Content Security Policy violation in a fresh Ember app

Today I created my first Ember App using the ember-cli:

ember new my-app
cd my-app
ember serve

so that it appears by url localhost:4200. I fail on the next step:

• Change content of the basic template application.hbs

After I perform some text changes I hit Cmd+S and reload the page the content remains the same. The browser console is "clean", but I get error messages in the terminal

Content Security Policy violation: {}

My environment: ember version: 0.2.3, node: 0.12.2, npm: 2.7.6.

I've searched for answers on Stack, but mostly they concern apps that have some external data requests, but my project is brand new and fresh, so I'm confused.

Looking forward to your replies, Thanks!