title: ValueError: Contour levels must be increasing - already sorted array
body: <p>I'm using matplotlib for contour plots and was able to have it working multiple times until now. For some reason, I now get the "ValueError: Contour levels must be increasing", but I have already sorted my levels array using <code>sort()</code>. I have tried many things and no results except this one error. I have no ideas as to why this was working and now is not.</p>
  
  <p>For reference, I have printed out the sorted array (has 4096 entries):</p>
  
  <pre><code>[-0.24418033 -0.20097393 -0.19743256 ...,  0.18904521  0.19392523 0.20172809]
  </code></pre>
  
  <p>Any help would be greatly appreciated! Thanks!</p>