Text input fields not work in flex when full screened

in Full Screen Mode due to security restrictions, in that someone could build a swf that spoofs some action on your machine... for instance displaying a mimic desktop that has a dialogue up asking the user to enter their live ID and password. There are probably loads of other sinister uses that adobe want to avoid by disabling keyboard input.

But If you're okay with using AIR instead of Flex you can run in full-screen mode with full keyboard input enabled:
Setting the displayState property of the Stage to StageDisplayState.FULL_SCREEN_INTERACTIVE places the window in full-screen mode, and keyboard input is permitted in this mode. (In SWF content running in a browser, keyboard input is not permitted). To exit full-screen mode, the user presses the Escape key.