Good news, bad news, and some other news.
On the good news front I can at least duplicate the problem in IE8. However there's no clear indication what is causing the problem, and it's likely to be deep in the plumbing. On the up side the file itself is actually uploaded (and the _exact_ same response is sent back in both cases.)
On the bad news front I'm not seeing any problem in IE 11 (or 10 or 9). So I'm not able to get the effect you are getting there. I'm using IE11 as my browser, and the F12 developer tools to put the browser into "Edge" (ie 11), 10,9 and 8 modes.
Are you sure there's a problem in IE 11 on your side? I'm going to update the javascript for the 8.33 build anyway - but I tried with the current javascript and no problems in 11.
Cheers
Bruce