实际上,官方给出了解决方案…
TinyMCE in a jQuery UI Dialog

// Prevent jQuery UI dialog from blocking focusin
$(document).on('focusin', function(e) {
  if ($(e.target).closest(".tox-tinymce-aux, .moxman-window, .tam-assetmanager-root").length) {
    e.stopImmediatePropagation();
  }
});