Nobody seems to make the remark that any digital system is a sample and hold. So wherever the marker is, between sample points it can move. But the display is a curve fit, it doesn't shows the hold.
The display is a
correct curve fit. It represents the DAC rate-of-change output of the system, which is the result of current
steering - this can't change instantaneously. The cursor represents the midway point between two held values, and it
can't move, because a movement would represent a bias towards one value or the other, which would be quite inappropriate.
But when you consider that for most of the time, people have some form of snapping set, generally the accuracy of where the cursor ends up, when looked at in minute detail, is way different from where they
thought it was anyway. But regardless of this, the midpoint between sampling points (at whatever sample rate you are using) is the finest resolution you can have from the system, and that's not going to change.