title: Matplotlib plot colorbar label
body: <p>I am trying to create a plot with a colorbar, with custom tick labels. When I try to create a label for a colorbar, it reverts to the original tick labels. </p>
  
  <p><img src="https://i.stack.imgur.com/CatNF.png" alt="output plot"></p>
  
  <pre><code>z = np.add(relzvals, shift_val)    
  
  fig=plt.figure()
  plt.contourf(x,y,z,25)
  ax = plt.colorbar()
  ax.set_label('cbar_label',rotation=270)
  ax.set_ticklabels(labels,update_ticks=True)
  </code></pre>
  
  <p>How can I get both customizations? </p>
  
  <p>UPDATE: For context, the main program require translated values, i.e.  <code>relzvals = z + shift_val</code>, and the matrix has to be translated back to <code>z</code> for plotting. </p>
  
  <p>I checked the values of <code>z</code> before coming inside <code>plt.contourf()</code> but it contains the original values. </p>
  
  <p>I have Python 2.7.11 and Matplotlib 1.3.1.</p>