Heatmap: extra tick added at the end of y-axis with categories enabled

[jedrzejruta]

Expected behaviour

The data points are aligned with categories correctly, no extra tick is shown.

Actual behaviour

There is an extra tick at the end of y-axis, resulting in an extra white space added at the top of the plot area.

Live demo with steps to reproduce

It seems to occur for data sets > 20, but also if the data set has 18 points, on initial load it also has an extra tick (the chart is redrawn correctly after changing it's size).
https://jsfiddle.net/BlackLabel/45xok289/

As a workaround, disabling the yAxis.endOnTick solves the problem: https://jsfiddle.net/BlackLabel/h8ng0q96/

Product version

Since the introduction of heatmap series (v4.0.0)