I see that this issue has been raised a number of times, but as far as I can see there has not been any resolution to it. So raising it again so that perhaps the developers can fix this issue. When selecting a line and setting Connected null values to never or threshold, the line still connects, as shown in this screen dump.
The same set data but with points in stead.
What I would expect is that the line is not connected when we select the options for it to not be connected.