Register you key listener on FlexGlobals.topLevelApplication.systemManager
Something like this:
FlexGlobals.topLevelApplication.systemManager.
addEventListener(KeyboardEvent.KEY_DOWN, manageUndoRedo);
FlexGlobals.topLevelApplication.systemManager.
addEventListener(KeyboardEvent.KEY_UP, manageUndoKey);
And in the functions check if the event.target is UITextField
This will listen for all the UITextFields even on the TitleWindows
