IE10 unexpectedly sends a HEAD request for PDF. What has changed?

I had a genuine problem. I am not the only one. While I researched the question, which was not obvious, I came upon the solution. I post the solution for whoever else has this issue.

My question gets closed as not a real question. What about this is not a real question?

I used the word unexpectedly: adjective not expected; unforeseen; surprising: an unexpected development., assuming that people would get that the question is why that suddenly has changed and not just close it because it missed an actual question mark

I can change the title to be more generic but that is about all I can see I could improve.

UPDATE: changed title from IE10 unexpectedly sends a HEAD request before handing PDF over to PDF viewer