AIR 27 - Alt-Enter toggles fullscreen; behavior not preventable

I'm seeing new, undesirable behavior in AIR 27. Holding the Alt key and pressing Enter (or Numpad-Enter) will toggle an application's fullscreen mode. (This wasn't the case with AIR 26.)

This behavior does not seem to be preventable; installing a keydown listener and calling preventDefault() does not prevent the behavior from happening.

stage.addEventListener(KeyboardEvent.KEY_DOWN, function (e :flash.events.KeyboardEvent) :void {
   if ((e.keyCode == Keyboard.ENTER && e.altKey) ||
        (e.keyCode == Keyboard.NUMPAD_ENTER && e.altKey)) {
       e.preventDefault();
   }
}, true);

Am I correct that this is a regression in AIR 27? Is there a workaround?