Minor ticks don't work with tickformat %Y and ticklabelmode period

Minor ticks don't work as expected when the following three axis properties are combined:

  xaxis: {
    tickformat: '%Y',
    ticklabelmode: 'period',
    minor: {
      ticks: 'inside'
    }
  }

The minor ticks don't show up. Changing the tickformat to anything below the year frequency (e.g. %b %Y) lets the minor ticks appear. Removing the ticklabelmode also makes the minor ticks appear.

Here is a codepen that demonstrates the issue:
https://codepen.io/Djeramon/pen/vYQzPOa
Expected behaviour: Minor ticks should appear.

It is unclear, why the minor ticks shouldn't work with a yearly frequency on the major ticks.

Commencez par la reproduction CodePen liée et vérifiez l’interaction entre yearly tickformat, ticklabelmode 'period' et minor ticks. Suivez les points d’entrée de la génération des ticks et du mode des libellés de l’axe afin d’identifier pourquoi les minor ticks sont omis ; le travail est terminé lorsque les minor ticks apparaissent avec les trois propriétés activées et que les cas existants continuent de fonctionner.