To reproduce:
- Add three line series and only set their point size.
- At runtime remove the second series.
- The points color is not updated corectly.

Workaround
- Set colors in code like this:
lineSerie1.BorderColor = Color.Red;
lineSerie1.BackColor = Color.Red;

lineSerie2.BackColor = Color.Green;
lineSerie2.BorderColor = Color.Green;

lineSerie3.BackColor = Color.Blue;
lineSerie3.BorderColor = Color.Blue;