got that yesterday, about ten times, probably corresponding to the number of occurrences, the same dialog prompting to allow flash player on a web page. And no, add-ons, plugins are not set to be "not virtualized".
edit: I know I could have avoided the multiple prompts by checking "do not show me..."... but it's just that there shouldn't have been any prompt at all, as flash player should have been sandboxed in the first place together with IE9.