Comment 2 for bug 1141551

I have this problem also in many Italian locos. I don't know if it is a bug of ORTS or if some parameters within the .eng file have an incorrect value.
In many locos I found such set of parameters
 AirBrakesMainMaxAirPressure( 75 )
...
 AirBrakesCompressorRestartPressure( 65 )
...
 EngineBrakesControllerMaxSystemPressure( 75 )
...
                       TrainBrakesControllerMaxSystemPressure( 75 )

If I set AirBrakesCompressorRestartPressure (and consequently also AirBrakesMainMaxAirPressure) to a value higher than the third and the fourth parameter, I can release brakes.
You can try setting e.g. AirBrakesMainMaxAirPressure to 100 and AirBrakesCompressorRestartPressure to 90.
I don't know if this is physically correct, but it works to me.