The change it's intentional, because when the height was set to 0, it prevented any vehicle to appear, while in some cases you want to remove the stairs only so, internally, GSX has a new setting, which cannot be controlled from the user interface.
We used this settings for the Aerosoft CRJ (which required it) so, we might add it to the GSX internal database to the default King Air, while we'll update the editor to expose this parameter to users.