Penultimate post on the AIR 1.5.2 update: Prior to AIR 1.5.2, if a user hit the escape key when an application was running in fullScreen or fullScreenInteractive, the application would be forced out of full screen mode. This remains the intended behavior for fullScreen, but was a defect in the implementation of fullScreenInteractive.
Starting with AIR 1.5.2, hitting escape causes fullScreenInteractive to exit by default but the behavior can be canceled by calling preventDefault() on the keydown event. Applications that use full screen to keep users (perhaps kids) from too easily leaving the application may find this change useful. As always, remember to update your namespace to take advantage of this new behavior.