I don't want to say 100% sure this is how it is working, but this is my guess without looking more into it. I've been avoiding just going and reading the code for some reason...

Here is what I would try if I was coding a stepper...

key goes on>
What position am I at?
No clue.
Step back a lot from where I am so I bottom out.
Now I know this is home, (typically closed all the way).
I'll call this "0".
Move to 150, which is 150 steps from 0.
(pulse 150 steps forward)
Now I'm at 150.
Move to 160, which is 10 steps further from here
(pulse 10 steps forward)
Now I'm at 160.
Move to 100, which is 60 steps backward from here
(pulse 60 backward)

... etc.

So, if you were to assume the MS does this, since I'm 95% sure these are not absolute positioning motors, it would have to do something similar. The only absolute positioning you can really run is if you define a home position first and keep track of where you are. (Hence the trouble with "moving only" setting, if it creeps around when unpowered, you lose track of where it is and can't position it anymore. "Always on" though is not great because it keeps torque on the motor, which usually means excess heat.