Visual Studio Development Server - CSS lost. On IIS Server is working

Visual Studio Development Server - CSS lost. On IIS Server is working

When I'm using Visual Studio Development Server
(http://localhost:64217/application) CSS gets lost and Chrome is showing
the following warnings and errors:
Resource interpreted as Stylesheet but transferred with MIME type text/html:
Uncaught SyntaxError: Unexpected token <
When using IIS server (http://localhost/application) the styles are fine.
I've checked these duplicate questions Visual Studio Development Server
not updating css and javascript? and Lose "modern" (CSS3) styles when
viewing on IIS vs VS Development Server [closed]. Unfortunately none of
them helped me.
I've tried clearing the cache and also didn't help. Any guesses what might
cause this to happen are very appreciated.
Also I have to mention that this happened today. Back in the past I was
using both IIS and Development Server and I didn't have this problem.
EDIT
I'm using Jquery Mobile and I've included the JQM CSS in the master page:
<link rel="stylesheet"
href="http://code.jquery.com/mobile/1.3.1/jquery.mobile-1.3.1.min.css"
runat="server" />
All the other CSS files are included in App_Themes/Default and included in
the web.config:
<pages theme="Default" />