I learned that IE11 looks for "browserconfig.xml" for pinned tile icons. So, if your site gets requests for that file, then blame IE11. Why Microsoft has to do this kind of crap?

"Note: If a webpage does not specify a browser configuration file, IE11 automatically looks for "browserconfig.xml" in the root directory of the server. To prevent this, use an "msapplication-config" header with the content attribute to "none" (shown earlier)." http://msdn.microsoft.com/en-us/library/ie/dn320426(v=vs.85)...