Incorrect trendline indicator recalculation after adding a point to main series

[kamil-musialowski]

Expected behaviour

After adding a point to the main series, trendline should recalculate all of its values to still remain as a straight line on a chart, indicating current trend.

Actual behaviour

Adding a point, results in incorrect calculation of the next trendline points.

Live demo with steps to reproduce

https://jsfiddle.net/BlackLabel/cd5403jh/

1. Click on add point and observe the black series (trendline).

Product version

Highstock + Indicators + Trendline v10.3.3

Internal note:
Checking older HC versions indicates that it never worked properly.