The FBW A320 parking brakes test has been fixed in yesterday's update, so you need to update and be sure you are not using a custom profile for it which might still contain the old custom parking brakes expression.
Nobody ever reported this problem with the PMDG 737 but, of course, it's difficult to say without knowing if you are using a custom profile for it that might have set the custom parking brake variable wrong for some reason so, even in this case, be sure you are using the GSX internal data, which is the only one we can assure works.