Burp

I was using backslash as a secondary engine cutoff key but found the same problem as you. And, like you said, saw no sign of it in the Settings menu. In the settings.cfg file though, the backslash key was bound to "CAMERA_MOUSE_TOGGLE" as it's primary key. I probably won't use CAMERA_MOUSE_TOGGLE so I changed it to "None" to disable it and now my backslash does what I tell it to do.