Adding a FontAwesome icon to window caption causes a broken image link

I am trying to add a FontAwesome icon to window caption. I used Window.setIcon method which accepts FontAwesome enumaration as paramater. However, it produces a broken link.

I checked the produced html. The following java code,
window.setIcon(FontAwesome.FOLDER);
creates

How can I fix this issue?

That seems to be a framework bug, I reported it:
http://dev.vaadin.com/ticket/14494#ticket