TinyMCE + ShadowDOM sadness

<!DOCTYPE html>
<html>

  <head>
    <script data-require="tinymce@4.4.3" data-semver="4.4.3" src="https://cdn.tinymce.com/4/tinymce.min.js"></script>
    <script src="script.js"></script>
  </head>
  <body>
    <my-element></my-element>
  </body>
</html>

class MyElement extends HTMLElement {
  connectedCallback() {
    const textarea = document.createElement('textarea');
    const shadowRoot = this.attachShadow({
      mode: 'open'
    });
    shadowRoot.appendChild(textarea);

    tinymce.init({
      target: textarea
    });
  }

  // does work without shadow DOM
  /*
  connectedCallback() {
    const textarea = document.createElement('textarea');
    this.appendChild(textarea);

    tinymce.init({
      target: textarea
    });
  }
  */
}

customElements.define('my-element', MyElement);

Example where TinyMCE throws an exception in postRender
because it cannot find sub-elements that are part of the
shadow DOM. This occurs even when passing in a direct
element to the init() function.

Open console to see exception details