Javascript Issues with Sharepoint 2010 and external CSS files

In Sharepoint 2010, I'm starting with the default master page and adding 1 external css file (the issue only seems to exist with css files from another domain) using a link tag. This does change the style correctly, however if I try to add a new announcement and select the main text box, t开发者_如何学Che ribbon controls become unresponsive. If I open the network tab in firebug, I can see that Sharepoint is constantly using an XMLHttpRequest to request the external css file I added. Is there anybody else that can confirm this bug or has any idea how to fix this problem?