Safari 14 input in shadow root arrow key bug

When an input is inside a shadow root, pressing the up/down arrows no longer moves the cursor to the start/end position.

HTML

<script>
  class InputTest extends HTMLElement {
    constructor() {
      super();
      this.attachShadow({ mode: 'open' })
      this.shadowRoot.innerHTML = '<input type="text">';
    }

    connectedCallback() {
      this.shadowRoot.querySelector('input').value = this.getAttribute('value');
    }
  }

  customElements.define('input-test', InputTest)
</script>


Standard element<br><input value="press up or down in Safari">

<br><br>

Custom element<br><input-test value="press up or down in Safari"></input-test>