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.

Inizia con la riproduzione CodePen collegata e verifica l’interazione tra yearly tickformat, ticklabelmode 'period' e minor ticks. Segui i punti di ingresso della generazione dei tick e della modalità delle etichette dell’asse per identificare perché i minor ticks vengono omessi; il lavoro è completato quando i minor ticks compaiono con tutte e tre le proprietà abilitate e i casi esistenti continuano a funzionare.