title: Dygraphs zoom synchronization resets y zoom of other
body: <p>I'm currently trying to plot some environmental data i.e. Temperature, Humidity and Pressure.
  I'm displaying 3 separate graphs and want their x-axis synchronized,but y-axis zooms synchronized (completely different ranges)</p>
  
  <p>I have set the graph up and everything works almost as expected, but:
  after zooming the y-axis of one graph, zooming any axis of another graph resets all graph y-ranges to the default/auto.</p>
  
  <p>Is there a way around this and is it possibly a bug or a feature? It can be seen at <a href="http://dygraphs.com/tests/synchronize.html" rel="nofollow noreferrer">http://dygraphs.com/tests/synchronize.html</a>, unclick the Range, and try zooming the y-axes of different graphs.</p>
  
  <p>The code:<br></p>
  
  <pre><code>var sync = Dygraph.synchronize(gs,{
      zoom: true,
      selection: true,
      range: false //disable y-axis sync
  });
  </code></pre>
  
  <p><a href="https://jsfiddle.net/svititom/e4da0L8o/1/" rel="nofollow noreferrer">https://jsfiddle.net/svititom/e4da0L8o/1/</a></p>
  
  <p>Thanks! </p>