Hi Guy,
What release are you running? It is always helpful to post relevant information. I am running X-Plane 11.20b3 on a PC with Win10. I am not seeing the issue you are talking about. Have you done anything to try to troubleshoot? If so, what steps have you taken?
The braking functions work fine for me - B, H, V. I know you don't want to try another keystroke, but for testing it might be worthwhile to rebind the command to another key just to eliminate any possible keyboard problem. If you are seeing the same problem with different keys, then it could be a SW issue unique to your config.
I do agree that the function should be renamed to Parking Brake.