Unexpected behaviour of plotly arrowhead on annotation

plotly.js
1

When defining the arrow end type of an annotation in Plotly, if I set arrowside: 'start', it seems to ignore the arrowhead setting.
Below is the annotation code, and an example on codepen where I duplicated the annotation, and only changed arrowside: "start".

annotations: [
    {
      x: 2,
      y: 5,
      xref: 'x',
      yref: 'y',
      text: 'If arrowside in set to start, the arrowhead seams to be ignored',
      showarrow: true,
      arrowhead: arrowhead,
      arrowside: "start",
      ax: 0,
      ay: -40
    },
    {
      x: 2,
      y: 3,
      xref: 'x',
      yref: 'y',
      text: 'If arrowside is omit or is set to end it work as expected',
      showarrow: true,
      arrowhead: arrowhead,
      arrowside: "end",
      ax: 0,
      ay: -40
    }
  ]

Am I doing something wrong, or is it a library bug?

Thank you!