This actually started happening to me a couple of weeks ago. i can drag the browser window over to my second monitor, go full screen with out issue, drop back to regular window and put it back on my main monitor and go full screen without issue several times until i close that page.
This only seems to be happening to me on hulu. youtube seems unaffected. And i just checked, commercials on huly work fine, it's the actual show that gives me the problems.
flash version is 10,3,181,34
browsers are ie8 and opera 11.50
on windows XP