I have a Lumia 925 with Dev Preview enabled and updated to GDR1. In my workplace we use authenticated proxy to connect to the internet through wi-fi. I set up the proxy server and the port on the connection advanced settings menu and I'm asked the username and the password on Internet Explorer, but after entering username/pw I just get asked again and again... I tested other phones (Android phones, iPhones and other Lumias) and all worked flawlessly, even my old Lumia 800 works with no problem.
I contacted our sysadmin, and he said he is able to see my phone making requests to the proxy server, but the requests have no info on password and username..
I guess this is a bug, since I'm using dev preview..
Anyone had a similar experience?