Afb Affects Brake Cylinder Pressure?

I have a problem with Afb on Dresden -Riesa route, driving BR146.
As soon as I press Afb on, the BC pressure goes up to 2.8 - 3.0 bar.
Whatever I am trying to do it, it just won't release until I don't turn Afb off.
Is this a bug? Or am I doing something wrong?
I attach a cab pic here where you can see all the levers.

 

That is prototypical; it should be on all German trains in-game but Dresden was the first actually to implement it. It's a safety feature; as soon as you give the beast 20N of tractive force, the brakes will release (sometimes they don't, but pushing the brake lever to release jogs them loose).

 

Thanks, I could start the loco now with Afb on.

 

Also from your picture, the AFB is set to 0 km/h, preventing you from releasing the brakes.