title: Group by label does not work
body: <p>I am trying to display three graphs in one panel. The graphs are counting new signups in dependency to the oauth provider. Why "facebook" and "email" is not showing up in the final graph? What am I doing wrong? </p>
  
  <p><a href="https://i.stack.imgur.com/Ob7vv.png" rel="noreferrer"><img src="https://i.stack.imgur.com/Ob7vv.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/uW4Gs.png" rel="noreferrer"><img src="https://i.stack.imgur.com/uW4Gs.png" alt="enter image description here"></a></p>