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.

リンクされたCodePenの再現から始め、yearly tickformat、ticklabelmode 'period'、minor ticksの相互作用を確認します。軸のtick生成とラベルモードのエントリポイントを追跡し、minor ticksが省略される理由を特定します。3つすべてのプロパティを有効にした状態でminor ticksが表示され、既存のケースが引き続き動作すれば完了です。