I have this problem: when I use, for example, the slider to control the radiator it goes in the last quarter from 50% to 0 without anything in between. 
In the VPC-Joy-setup is shows that the dial, slider and z-axis are at 74%-ish when centered.
I have found no way to re-calibrate them in order that at the center of those axis's (right at the bump) the value is 50%.

Any MT50 user with a solution?

Yeah.  You probably upgraded firmware recently?

Go into DIView, right-click on that axis, calibrate.  Then hit "reset to defaults".

What can happen, if you happen to have a failed calibration, the the end point values can get screwed up.  If an end point gets a number in it that's less than a value that's somewhere in between, it will "jump" back once you surpass that number.

Setting it back to defaults will make the low end 0, the high end 4096, and the middle 2048 (or something like that).  You can readjust the calibration after that once it's working again, if necessary.

I’m away from home right now. Tomorrow I will do the reset.