title: Flask wtform RadioField label does not render
body: <p>When using the following form:</p>
  
  <pre><code>class TextForm(Form):
      example = RadioField('Choice 1:', choices=[('A','Option A'),('B','Option B')])
      key = RadioField('Choice 2:', choices=[('1', 'Option 1'), ('2', 'Option 2')])
      submit = SubmitField('Submit')
  </code></pre>
  
  <p>I am expecting to see:</p>
  
  <p>Choice 1:</p>
  
  <ul>
  <li>Option A</li>
  <li>Option B</li>
  </ul>
  
  <p>Choice 2:</p>
  
  <ul>
  <li>Option 1</li>
  <li>Option 2</li>
  </ul>
  
  <p>Instead I am getting no labels as follows:</p>
  
  <ul>
  <li>Option A</li>
  <li>Option B</li>
  <li>Option 1</li>
  <li>Option 2</li>
  </ul>
  
  <p>What am I missing?</p>