One side affect of Sysprep is that a user may be forced to change/update the Local Administrator password. You can assign a post customization script to turn this off,
it's a "net ..." something command that states admin doesn't have to change it's password post sysprep.
If you did have the "Update Local Admin" password enabled, with generate password, then that should be the password after running Guest Customization.
If you don't want this changed, you have to deploy a copy of the vApp to My Cloud ... disable the setting while it's powered off, then capture the vApp back to your Catalog to store the new settings.
If the settings are not retained in copying the vApp back to catalog, then you should upgrade to vCloud Director 5.1.2.