I found in my case if I went back a page or two the quiz would count those questions again, it would also recount questions if you just refreshed the page and took the test over. At one point I had 47 questions right. The only way to keep a correct score was to close the page out and then come back to it.
As LadyF found out it seems the quiz page isn't written properly in order to handle cookies or cache. By the way, I had no problems doing the quiz with IE10.
If you read LadyF's post#26
there was a reason specific to her.