Why vue need to forceUpdate components when they include static slot

constructor (props) {
  super(props);
  this.state = {
    questions: [<TextBox key={0}/>]
  }
  this.createTextBox = this.createTextBox.bind(this);
  this.loadTextBox = this.loadTextBox.bind(this);
}

createTextBox() {
  const newQuestions = [...this.state.questions, <TextBox key={this.questions.length}/>]
  // or you can use 
  // const newQuestions = this.state.questions.concat(<TextBox key={this.questions.length + 1}/>)
  this.setState({questions: newQuestions})
}

loadTextBox() {
  return (this.state.questions);
}