dedicated "Insert Macro" not regarding "cssClass" parameter

I tried the new feature adding macro buttons into to ckeditor toolbar. All is working fine, but the "cssClass" parameter is not recognized for the box macro.

config['xwiki-macro'].insertButtons = [
  {
    commandId: 'box1',
    macroCall: {
      name: 'box',
      parameters: {
        title: 'test',
        cssClass: 'testClass'
      }
    }
  }
];

So the title parameter is populated the cssClass parameter not.