Ricardo's suggestion is good . He has taken the time to try and help you.
If you don't try to see which keys on your setup are assigned to the Park Brake , you may never find the solution.
Given that the park prake is a progressive function when operated by mouse , just like the throttle , how do you know there is no cross talk unless you check ?
Checking the assignments of key strokes ,throttles ,buttons etc is always a good idea , I have found that a command assigned to two different keyboard letters or a throttle quadrant & keyboard may and often do cause unexplained behaviour.
As an example , if I use my throttle lever on the CH throttle quadrant and there is a throttle assignment on the keyboard the throttle response in game is occasionally very odd.