How to diagnose issue with IE 11.0.9600.17207 up/down-loading a file

(It could be that this belongs on SO; I can't figure out how to work out if it's a code issue or something else).

I have a server running:

• Debian 7.6
• nginx 1.6.0
• uWSGI 1.9.16
• Django 1.6.5

I have code that does this:

1. accepts a form post containing a Word (application/vnd.openxmlformats-officedocument.wordprocessingml.document) file
2. processes the file creating a new Word file
3. returns the new file

This works fine in Safari, Firefox, Chrome, etc. It works fine in IE<10. It works fine in IE 11.0.9600.17126, update version 11.0.9 and earlier versions of IE 11.

In IE 11.0.9600.17207, update version 11.0.10, it does not work (tested on multiple computers, all Windows 7, some in a domain, some not). The page in IE is non-responsive; there's no timeout (for several minutes at least) or error (the spinner is still spinning and the close tab button works). In the network activity section of the developer tools it just shows as pending. Changing the User-Agent string doesn't make any difference.

The code executes at least as far as the return in the view handler. There's nothing in any of the code that behaves differently depending on the browser/user-agent.

How can I diagnose what is happening here? Is there a way to tell whether IE understands that it has finished sending the file? Or to know whether it is trying to get the response, or whether it has received any response? This is all over SSL, although I could temporarily disable that if necessary. Is there something special that needs to be done with nginx/uWSGI/Django to handle this latest version of IE?