Interesting, I've never exported JSON from C2, though I am a regular user of IE11. So to simplify your query, the problem line is...
function 15: "download as JSON data with filename "questionPool.json"
so I ran your capx and the file I was asked to download was the following. So I hate looking and converting all of this crap to normal text, but to me it seems like this is the correct json file but IE11 is trying to open it with an app, and when it can't, it's trying to parse it as a weblink and failing. If I configured an app to view this, I think it'd behave the same as FIREFOX. Chrome and Firefox see this and interpret it as json and hence you don't see the headers as they strip them out. So I suspect if you could get rid of all the hex encoded text you'd get the file that you wanted.
JSON is built in IE11 but apparently there are some issues on how the file is configured to ensure it is handled correctly. So it is an issue with IE11 and not C2, and there are fixes for IE11 for this available or so a quick google search suggests.
you wanted to get
and you got