title: d3 opacity transitions flash final state
body: <p>I have a number of basic opacity transitions along the lines of</p>
  
  <pre><code>emp_line.transition()
      .duration(1250)
      .attr('opacity', 1)
  </code></pre>
  
  <p>However, when I run them, often these items will flash to full opacity and then back to none and fade in. Is there any way to prevent this content flickering?</p>