Please remember the older bus braking systems are different!!
The MCI D Coach has a different type of braking system called a DD3 Brake system. This system requires a full brake application before the vehicle parking brake will release. Please watch the associated video for details. As a side note, this process can be used as a habit to ensure brakes are always properly released across manufacturers and types.
DD3 MCI Brake Systems from Transportation Safety Systems on Vimeo.