[devsatish]

reading the lines, It seems this is only in the Metro version of IE. But still an hassle, where the desktop IE pops-up when non white-listed Flash content is on the page.

Submitting your site for consideration for Internet Explorer compatibility As stated previously, developers who have sites that require Flash Player can mark the page with a META tag (or serve a header) indicating that the site requires a plug-in. This causes Internet Explorer 10 to prompt the end user to open the site in Internet Explorer 10 for the desktop. If a site is on the CV list as compatible with Internet Explorer 10, Internet Explorer 10 will always open it with Flash Player enabled and the user won't be prompted to open in Internet Explorer 10 for the desktop.