This is how its supposed to work. In a properly calibrated madVR system with Full RGB output, you're not supposed to see 0-15 or 236-255. 16 is black, and anything below is also black, and 235 is white, and everything above as well. It'll use the full rgb range of 0-255 to represent these values, so that your display gets 0 as black, and 255 as white, anything between 0-16 is then "lost", but there isn't really any information there anyway (some people will argue there is, but on a properly calibrated display you wouldn't be able to see them anyway, so whats the point? unless you sacrifice black or white level to be see BTB or WTW, which is a bad idea as well)
If you then calibrate your display so that you can just barely make out differences between 16 and 17 (go down to where there is no difference anymore, and then slowly go up until you can just make out a difference), and the same for 234/235, then you're done, and have a properly calibrated display.