When will the BrakeControlSpeed work?

In the documentation it says:

A non-negative floating-point number measured in kilometers per hour (km/h) at which the brake control system changes operation. The setting is ignored if BrakeType is set to 2 or if BrakeControlSystem is set to 0. See the description for BrakeControlSystem for more information.

But in the code of the game it says:

if (a != 0 && BrakeType == TrainManager.CarBrakeType.AutomaticAirBrake || ElectropneumaticType == TrainManager.EletropneumaticBrakeType.DelayFillingControl){
Interface.AddMessage(Interface.MessageType.Warning, false, "BrakeControlSpeed will be ignored due to the current brake setup at line " + (i + 1).ToString(Culture) + " in " + FileName);
break;
}

Well, there is a mismatch! What is it actually designed to do? To disable it when the BrakeControlSystem is set to 0, or to 2?

This variable will be ignored under any of the following circumstances:

• The variable itself is set to zero (disabled)
  
• The BrakeControlSystem variable is set to 2 (Delay-including control)
  
• The train is using automatic air brakes. (Brake type set to 2)
  

The conditional appears right to me; It's evaluated in two parts:
a != 0 && BrakeType == TrainManager.CarBrakeType.AutomaticAirBrake


This triggers if we are using automatic air brakes, and the variable contains a non-zero value. (If zero, it's disabled, hence no need for the error)

ElectropneumaticType == TrainManager.EletropneumaticBrakeType.DelayFillingControl

This triggers if the electropnuematic type is set to delay filling control. For completeness, there probably ought to be a non-zero check here too, but with this variable set the BVE2 / BVE4 train editor IIRC omits the line altogether.

BrakeControlSpeed is supposed to set the lowest speed at which the train is still able to use dynamic brakes (in BVE it means motors providing brake force and (in openbve) MOTOR_B1/B2 sounds playing at a volume proportional to that force, apparently), this is sometimes called "Regeneration Limit" (somewhat incorrect, as just dynamic brake "dumping" energy thru resistors/gearbox in terms of physics and sound is similar), braking below that speed will only use pneumatic brakes (in reality this speed is often set at the point when dynamic brakes become considerably less efficient). And all brake control systems (except "None" or when automatic air brake is specified) use that value.

Closing electromagnetic valve: trailer cars use air brake, motor cars use only dynamic brakes until the speed drops below BrakeControlSpeed, when dynamic brake turns off and gets replaced with air brake at the same BC pressure as on trailer cars for that notch.

Delay-including control: similar to the above, but at higher brake notches (apparently above 3/4 brake, as I noticed that at, for example, 4th notch for 4-notch handle and 7th and 8th notches for 8-notch handle) air brake is blended in (typically at much lower pressure compared to trailer cars, as dynamic brakes keep operating), and dynamic brakes keep working even below BrakeControlSpeed (but at that speed BC pressure on motor cars equalizes to that of the trailers).

These are the few options availiable in openbve, BVE5 format allows for more detailed tuning (setting pressures for every notch, separate delays for air brakes and dynamic brake, more realistic brake system algorithms, etc)