title: Unexpected underscore in git log --graph output
body: <p>When running <code>git log --graph</code> on my copy of the Linux kernel, I'm seeing an underscore in the graph that doesn't look like it should be there. </p>
  
  <p>What does that underscore mean?</p>
  
  <p>The specific command I'm using is thus:</p>
  
  <pre><code>git log --graph --decorate --pretty=oneline --abbrev-commit --all --date-order
  </code></pre>
  
  <p>And the output looks like this:</p>
  
  <p><a href="https://i.stack.imgur.com/E4xNk.png" rel="noreferrer"><img src="https://i.stack.imgur.com/E4xNk.png" alt="git log --graph output"></a></p>
  
  <p>I've tried looking at this area in the graph in gitk, but there doesn't seem to be anything out of the ordinary there.</p>
  
  <p>I don't <em>think</em> this is just showing a branch point, as I'd expect that to be rendered as on the right, not as on the left (the left should match the image above):</p>
  
  <pre><code>I see:        I'd expect for
                normal branching:
  
   \ \ \         \ \ \
   / / /         / / /
  | _ /         | / /
  |  /          |/ /
  | |           | |
  | |           | |
  </code></pre>