This is based on my experience using a gamepad and assigning controls through the in-game Controls->Keyboard->Multi-Click Settings

Brakes do not appear in the default list of commands, nor can you assign "+brakes" to either a long press or short press when using multiclick settings. It does work if you assign the brakes in the regular keyboard or gamepad menus, so this bug seems specific to the multiclick settings. In contrast, I can assign something like +turbo to a long press in the multiclick settings with no issue.