In the case when I want to show a flash movie over a PDF file, it is just fine if I use IE9, 8, and 7. Firefox and Mac Safari also shows no problem. But Windows 8 + IE 10(desktop mode) shows only PDFs in the case of the test page:
http://www.broadband-xp.com/test/ie10/zindex_test.html
The flash file is behind the PDF.
Notice: I am not talking about Modern Style IE10. It is just by the design that Moden Style IE10 does not support displaying PDFs within the browser.
And it seems that Windows 7 + IE10 preview does not have this bug.
I reported this issue to Microsoft Connect,
https://connect.microsoft.com/IE/feedback/details/769989/desktop-mode-ie10-ignores-z-index-value-in-the-case-of-pdf
But it was closed as "won't fix", with Microsoft's comment that "At this time we do not plan to fix this issue. ... We will consider fixing this issue in the future."
But I want this problem to be fixed as soon as possible.