I have multiple systems running Windows 8.1 Update - all fully patched. All virus free and with no add-ons or toolbars installed.
On one system, IE11 won't download anything unless I "run as administrator" for IE11. There are other postings with a similar issue on the internet - but no resolution.
If I go to, for example, the MS download site and click on anything and try to download (for example) Test.exe - the file is renamed "test_exe" and it fails to download. Ditto any other site where I download from a link (including from my own server).
Indeed, SuperUser.Com doesn't work correctly - the login button having no effect other than to refresh the page - unless I "run as administrator" on IE11.
On my other machines it works fine.
There obviously is a difference between them, but I don't know what - I've just restored an image of a clean install and then re-patched it and the same issue arises.
Most IE settings are set via Group Policy.
I found this similar problem here http://www.eightforums.com/general-support/33509-trouble-downloading-using-internet-explorer-11-a.html
I have UAC turned off on my machines - but turning it on makes no difference either.