Never mind... fixed it myself. Had to set XValues order to "none". Sorry for the false alarm!

I have an application where I use hidden points as a trick to diplay multiple data traces in a single series on a line plot. Specifically, I have (say) x-axis coords which range from 0 to 10 and 3 different y values for each x value. I know this could be done with 3 separate series, but for various ...