Yes, your observations are correct, it seems the parameters have a greater resolution than the panel displays (or can be adjusted on the GUI).
The default value for voice 2 for example is set to 0.2480, which displays as 0, though is not quite, so when you move it away and back to 0, it then does go to zero.
You can only set these fine values if your DAW lets you look at it as a generic editor view (that's what Cubase calls it anyway), but there are so many values in Matrtix 12V, you really don't want to be looking at it this way !
So, put this down to a quirk of operation, rather than a bug.