The thread Classic UI 1.8 RC appears to be the same problem. I also see this in chrome’s console:
GET https://192.168.1.2:8443/%22https://192.168.1.2:8443/classicui/WebApp/Design/Img/loader-gray-100x12x2.png%22 404 (ProxyServlet: /%22https://192.168.1.2:8443/classicui/WebApp/Design/Img/loader-gray-100x12x2.png%22)